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IOE Dentistry - Saliva > Organic components of saliva > Flashcards

Organic components of saliva Flashcards

1
Q

What is the average range of the total amount of protein found in saliva?

A

Approx 1-6 g/L

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2
Q

What factors affect the total salivary protein content?

A

Total salivary protein content varies according to flow rate and relative contribution from different salivary glands

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3
Q

What are the salivary proteins broadly categorised into?

A

They are categorised according to function:

  1. Proteins with lubricating properties
  2. Proteins with anti-microbial properties
  3. Enzymes
  4. Proteins with mineral binding properties.
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4
Q

What are the 7 main salivary proteins?

A
  1. Salivary mucins
  2. Statherin
  3. Proline rich proteins
  4. Histatins
  5. Immunoglobins (antibodies)
  6. Enzymes
  7. Lactoferrin
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5
Q

What are salivary mucins?

A

Salivary mucins are glycosylated proteins containing more than 40% (sometimes as much as 80%) carbohydrate on a weight basis.

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6
Q

What are salivary mucins important for?

A
  1. Mucins are important lubricants in the mouth

2. They protect the hard and soft tissue surfaces from damage

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7
Q

How many of the salivary proteins are salivary mucins?

A

25%

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8
Q

How and why are salivary mucins good lubricant?

A

The lubricant properties of these salivary glycoproteins is directly related to their structure

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9
Q

What is the structure of salivary mucins?

A

Carbohydrates are added to proteins by covalent attachment to the amino acid side chains. Two types of attachment are found, O- and N- linkages
his occurs after the polypeptide chain has been synthesised, via specialised enzymes in the endoplasmic reticulum and Golgi and is an example of protein post-translational modification.

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10
Q

Which sugar linkage is more abundant in salivary mucins: O or N linked mucins?

A

O type linkage is far more abundant

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11
Q

What are O- links sugars added to?

A 
To serine (SER) or threonine (THR) amino acid residues within the mucin polypeptide chain via their side chains, which both terminate with an hydroxyl group. 
This forms a O-linkage result
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12
Q

What are N- links sugars added to?

A

N-linked sugars are attached to the amide nitrogen of the side chain of asparagine (ASN) residues within the polypeptide chain

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13
Q

Where are carbohydrates added?

A

Carbohydrate is only added to asparagine side chains where the asparagine occurs as part of the sequence asparagine-other amino acid-threonine or serine.

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14
Q

What do we call a sequence which tells the enzymes to add a modification to the amino acid?

A

A consensus sequence

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15
Q

What are carbohydrates attached via N- type linkages usually?

A

Oligosaccharides

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16
Q

What do oligosaccharides contain?

A

more than one carbohydrate residue

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17
Q

What is the one thing all oligosaccharides have in common?

A

They all share a common core structure, based upon N-linked N-acetylglucosamine where further sugars are then attached to
They may have a different number and types of carbohydrates attached

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18
Q

What are some examples of some oligosaccharides?

A

Sialic acid (N-acetylneuraminate) is frequently part of the oligosaccharide structure in salivary mucins

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19
Q

What does the presence of substituted carbohydrates like sialic avid confer?

A

The presence of substituted carbohydrates such as sialic acid confers a negative charge on salivary mucins and results in an extended structure for the proteins in solution due to repulsion of charges.

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20
Q

What do mucins compromise of?

A

Carboxyl- and amino terminal domains that are rich in cysteine (CYS) residues which are capable of forming covalent cross links through their sulphydryl (-SH) side chains
In this way, more than one of these monomeric structures can be linked together, in a linear fashion, to form mucin oligomers.

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21
Q

What are oligomers?

A

More than one mucin monomer linked together?

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22
Q

What is the large central portion of the salivary mucin MG1 made of?

A

The large central portion of the molecule is formed of multiple repeats of 10 to 80 amino acid residue sequences in which up to half of the amino acids are serine or threonine. This area becomes saturated with hundreds of O-linked oligosaccharides.

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23
Q

What are the 2 types of salivary mucins called?

A

MG1

MG2

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24
Q

Describe the MG1 salivary mucin

A

Is a high molecular weighted mucin
Is a picture of 3 different gene products
Is an oligomeric structure with a molecular weight greater than 1MDa
MG1 form complexes with other salivary components including amylases, proline-rich proteins, statherin and histamines and human defence peptides

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25
Q

Describe the MG2 salivary mucin

A

Derived from a single gene
Is a single monomer with molecular weight of around 250kDa
MG2 bind to oral pathogen and genes like oral Streptococci and there periodontal pathogen (Actinobacillus actinomycetemcomitans)

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26
Q

What is similar about both MG1 and MG2?

A

They are both produced in different amounts by the major and minor salivary gland

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27
Q

What does the MG in MG1 and MG2 stand for?

A

MG stands for mucous glycoprotein)

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28
Q

What are the 6 functions of salivary mucins?

A
  1. Protections for oral surfaces against Dissection
  2. Lubrication of hard and soft tissues to protect from mechanical damage and to facilitate in speech and swallowing
  3. Provide a barrier to microbial colonisation (In addition, purified MG2 has been shown to kill oral bacteria as well as the opportunistic yeast,)
  4. Role in regulation of other salivary proteins and peptides
  5. Anti microbial and anti fungal activity
  6. Direction of bacterial colonisation.
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29
Q

What are the functions of Statherin?

A
  1. Protects against ectopic calcification within the oral cavity by inhibiting the spontaneous precipitation of hydroxyapatite mineral.
    tatherin binds to hydroxyapatite mineral and inhibits its growth. In addition, it binds calcium and so prevents the spontaneous precipitation of hydroxyapatite, reducing the possibility for calculus formation.
    Statherin is an important component of the salivary pellicle – the thin protein-rich deposit which cover the surface of the teeth.
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30
Q

What can happen if there are too many mineral ions in saliva?

A

high concentration of mineral ions in saliva could lead to unwanted deposition of mineral if uncontrolled.
Calculus (calcified plaque or tartar) can build up leading to periodontal (“gum”) disease and stones can block salivary gland ducts

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31
Q

What is the nature of the primary structure of Statherin?

A

It has an asymmetric nature

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32
Q

Describe the primary structure of statherin

A

The amino terminal of the molecule is highly charged, with five consecutive amino acids with side chains that are negatively charged at physiological pH

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33
Q

Which section of the primary structure of statherin binds to calcium and why?

A

Amino acid residues 1-6 bind calcium tightly and so prevent spontaneous precipitation of hydroxyapatite from saliva.

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34
Q

Describe the secondary structure of statherin

A

Statherin has an unusual secondary structure because it contains a relatively high proportion of the imino acid PROLINE (PRO) precluding the alpha helix structures found in many other proteins.

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35
Q

What does the whole statherin molecule bind to in saliva and what does this binding do?

A

The whole of the Statherin molecule binds to existing hydroxyapatite mineral and inhibits further crystal growth

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36
Q

What role do proline rich proteins (PRPs) have in saliva?

A

They control mineral crystal growth and are important components of the salivary pellicle

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37
Q

What is the salivary pellicle?

A

The thin protein-rich deposit which covers the surface of the teeth.

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38
Q

What proportion do Protein rich proteins make up of the total salivary protein

A

PRPs make up 10-40% of the total salivary protein

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39
Q

Where is there a rich supply of proline rich proteins?

A

The sub mandibular gland

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40
Q

Other than in saliva where else are PRP found?

A

PRPs are also found in the secretions of the trachea and pharynx

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41
Q

Where are proline rich proteins derived from?

A

Proline rich proteins are polymorphic and derive from a group of genes situated on chromosome 12

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42
Q

How many proline rich proteins have been identified?

A

Six different PRPs have been identified so far, all closely related in respect of their primary structure.

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43
Q

What is the average concentration of proline rich proteins in saliva?

A

approx 50 mg/100mL

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44
Q

State 3 characteristics of proline rich proteins

A
  1. They have a high negative charge
  2. They are distributed asymmetrically
  3. They are acidic
45
Q

What are the functions of PRP?

A
  1. Inhibition of HAP growth (res 1-30)
  2. Interact with oral micro organisms (COOH terminal interacts with bacterial cell walls)
  3. Exclusion of pathogens from the dental surfaces by binding to the mineral

The full function and significance of the PRPs is probably as yet unrecognised.

46
Q

What do we know about the amino terminal in PRPs?

A

We know from experimental evidence that the amino terminal of the PRP (which is negatively charged) is able to bind to existing hydroxyapatite mineral and inhibit its growth

47
Q

What do we know about the COOH terminal in PRPs?

A

able to interact with bacterial cell walls in a specific way

48
Q

How do PRPs stop bacterial colonies forming on the dental surface?

A

By binding to the mineral and interacting specifically with benign micro-organisms, favouring their colonisation of the tooth surfaces over that of pathogens

49
Q

What are histatins?

A

Histatins are a group of small, defence-peptides which are rich in the amino acid histidine.

50
Q

What is the side chain of histidine and what is its pK?

A

side chain= Imidazole ring

pK= approx 6

51
Q

What is the side chain of histatins capable of doing?

A

The imidazole ring is capable of being protonates via the nitrogen of the ring to give charge of plus 1

52
Q

Describe histatins at pH 6

A

At pH 6, half of the side chains will be protonated (+) and half will be neutral

53
Q

What gives histatins their basic characteristics and how?

A

They contain the amino acids arginine (ARG) and lysine (LYS) which have side chains which are positively charged at physiological pH.
Histatins are therefore basic proteins

54
Q

What is the pKa of histatins and what does this mean?

A

pKa is close to neutral this means Histatins are probably the only salivary proteins with significant buffering potential.

55
Q

What is the concentration of histatins in saliva?

A

Relatively low

The conc in the parotid and mandibular saliva is approx 3mg/100L

56
Q

What are the 6 inhibitors of histatins known to be?

A

They are known to be potent inhibits of Candida (yeast)

57
Q

What are the functiosns of histatins in saliva?

A

Their function have been related to anti- candida activity
They are also known to have some activity against Streptococcus mutans (associated with dental caries)
Histatin-1 binds to calcium and prevents hydroxyapatite precipitation.

58
Q

How many classes of immunoglobulins are there?

A

5
There are five different classes of immunoglobulin, differing in their respective structures and roles. Three of these classes are routinely detected in saliva.

59
Q

What are the 3 difference classes of immunoglobulins found in saliva and what do they all have in common

A
  1. IgM
  2. IgG
  3. IgA.
    All share a basic monomeric structure based upon a Y shaped molecule comprising of 4 polypeptide chains.
60
Q

Describe the structure of IgG

A

IgG comprises of a single Y shaped molecule

61
Q

Describe the structure of IgM

A

IgM is a pentameric structure made up of 5 such Y shaped molecules.

62
Q

Describe the structure of IgA

A

IgA is a dimer, with 2 Y shaped molecules attached end-to-end by a small poylpetide chain.

63
Q

Which of the 3 classifications of immunoglobulins is the most important and most abundant?

A

IgA

64
Q

What concentrations of IgM and IgG are found in saliva?

A

They are found in trace amounts only in saliva and may arise as “contaminants” from the outflow of fluid that exudes at the gingival margin

65
Q

What is the fluid found at the gingival margin called?

A

This is a serum-derived exudate, called gingival crevicular fluid (GCF) which seeps out in to the mouth, especially where inflammation of the gums is present.

66
Q

From where is IgA secreted from?

A

IgA is secreted directly into saliva via the epithelial cells of the salivary gland.
During its transport through the epithelial cells, it picks up an additional polypeptide chain called the secretory component which wraps itself around the molecule and confers some degree of protection for IgA in the hostile environment of the mouth.

67
Q

What is the difference between IgA found in the saliva and IgA found in the blood?

A

IgA circulating in the blood and tissue fluid does not contain the secretory component and we call it “Secreted IgA” (o sigA)

68
Q

Where is sigA found other than blood and issue fluid?

A

Also found in other secretions such as tears or the secretions of the gut and urino-genital tract
thought of as “the first line in defence”

69
Q

What is the function of all immunoglobulins?

A

The function of all immunoglobulins, including sIgA is to recognise invading pathogens, bind to them and bring about their elimination from the body.
Bacterial agglutination

70
Q

What happens when immunoglobulins bind to their specific bacterial protein?

A

Every immunoglobulin is very specific in its binding capabilities and will therefore target specific bacterial proteins only.
When immunoglobulins bind to their targets (antigens), they form precipitate-like structures by cross-linking (bridging) between more than one bacteria. This is called “agglutination” or “clumping”. The bacterial-immunoglobulin complex can then be swallowed and removed

71
Q

What was amylase called before?

A

Ptyalin

72
Q

Describe salivary amylase?

A

Salivary amylase is calcium-dependent and activated by chloride ions.

73
Q

What is the concentration of amylase in stimulated saliva?

A

Around 0.5 grams per litre but the concentration of amylase varies with flow rate

74
Q

Where is salivary amylase secreted from?

A

Most of the enzyme is secreted by the parotid (it accounts for 1/3 of the parotid salivary proteins)

75
Q

What are the functions of amylase?

A

Digestion of carbohydrates

Enzyme can catalyse the hydrolysis of the alpha 1-4 glycosidic bonds between glucose residues

76
Q

What can we see amylase do aside from digesting carbohydrates?

A

It is known to bind to tooth mineral and was recently detected in carious lesions of enamel, though we don’t know what it might be doing there.

77
Q

What can salivary amylase not break down?

A

It cannot brad down maltose but is able to break down long glucose polymer chains into their glucose monomers
Also can’t break down other glycosidic links, such as alpha 1-2 or alpha 1-6. It therefore cannot break down sucrose or the complex branched polysaccharides that are found in bacterial plaque.

78
Q

Where is amylase also found aside from the saliva and pancreas?

A

Amylase is also found in other secretions, such as tears and bronchial and urinogenital secretions
Unlikely to have a digestive function so possible that the full roles of amylase are not yet known.

79
Q

Which enzyme is an important in anti microbial?

A

Lysozyme

80
Q

Describe lysozyme?

A

It a muramidase enzyme which is also found in many other exocrine secretions.

81
Q

What does it mean to be a muramidase enzyme?

A

Muramidases are able to catalyse the hydrolysis of the bond between N-acetylmuramic acid and N-acetylglucosamine, which are components of bacterial cell walls.

82
Q

What are bacterial cell walls typically made up of?

A

Bacterial cell walls are typically made up of long polysaccharide chains which are cross-linked together by short peptide linkers.
This forms a mesh-like sac or bag-like structure which surrounds the bacteria.
The long chain polysaccharides are polymeric structures of a repeating disaccharide comprising of N-acetylmuramic acid and N-acetylglucosamine, which are joined together via an alpha 1-4 glycosidic link.
It is this bond which is hydrolysed in the presence of lysozyme.

83
Q

What happens when the bacterial cell wall is digested?

A

This leads to bacterial lysis and death

84
Q

What do some bacterial cells have to protect them from the effects of lysozyme?

A

Some bacteria have protective coatings on their cell walls which confer resistance against lysozyme by restricting access to the target substrate in the cell wall.

85
Q

What has been suggested lysozyme works with?

A

It has been suggested that lysozyme acts co-operatively with sIgA, lysing bacterial cells which have already been recognised and “tagged” with bound sIgA

86
Q

What can lysozyme do to some bacteria aside from digesting their cell walls?

A

Lysozyme is also known to cause aggregation of some bacterial species, resulting in agglutination

87
Q

What can lysozyme bind to aside from bacteria?

A

Lysozyme binds to hydroxyapatite mineral and is one of the proteins found in the salivary pellicle

88
Q

Name some salivary enzymes we need to know about?

A
  1. Amylase
  2. Lysozyme
  3. Salivary perioxidaase
  4. Acid phosphastases
  5. Esterases
  6. Glucuronidases
  7. Carbonic anhydrase
89
Q

What is salivary peroxidase alternatively known as?

A

alternatively known as sialoperoxidase

90
Q

What does salivary peroxidase do?

A

It catalyses the reaction between hydrogen peroxide and thiocyanate to generate the hypothiocyanite ion and other oxidised derivitives.

91
Q

How is hydrogen peroxide present in saliva?

A

It is a product of bacterial metabolism

92
Q

How is thiocyanate present in saliva?

A

It is present in saliva from dietary sources such as cabbage and certain fruits and from cigarette smoke

93
Q

What is an advantage of removing hydrogen peroxide ?

A

Hydrogen peroxide would be a source of free oxygen radicals which are extremely damaging to soft tissues id it builds up in cells

94
Q

What is an advantage of removing thiocyanate?

A

Build up of thiocyanate can be toxic to cells

95
Q

What is a benefit of producing the hypothiocyanite ion?

A

It is extremely toxic to bacteria via their inhibitory effects on bacterial metabolic enzymes used in energy production.

96
Q

What are the 2 main functions of salivary peroxidase?

A
  1. Important detoxifier (must remove hydrogen peroxide to prevent free radical formation)
  2. Role in protecting soft tissues and periodontal disease
97
Q

What is lactoferrin?

A

It is a a salivary antimicrobial protein

98
Q

What do lactoferrin do?

A

Lactoferrin sequesters (binds) ferric ions (Fe three plus) which are essential bacterial nutrients.

99
Q

Why are lactoferrin important?

A

, lactoferrin acts an important anti-microbial, depleting iron in the local environment and making it unavailable for bacterial use. It has been shown to have a direct bactericidal effect on some micro-organisms, including Streptococcus mutans strains which are implicated in the caries process.

100
Q

What are lactoferrin susceptible to?

A

Lactoferrin is susceptible to degradation by certain bacterial proteases and one type of bacteria (a spirochaete of the Treponema family) is able to actually transport lactoferrin into its cell and use the bound iron for its own nutritional purposes.

101
Q

Name 2 small molecules that are present in saliva and are useful pH rise factors?

A

Urea

Tetrapeptide sialin

102
Q

What are both urea and tetrapeptide sialin metabolised by?

A

Both sialin and urea can be metabolised by the plaque micro-organisms to produce ammonia, neutralising plaque acid.

103
Q

What is an unwanted side affect of the metabolisation of tetrapeptide sialin?

A

Unwanted by product is putrescine
a molecule which originally derives from arginine (ARG), and, as its name suggests, can contribute towards halitosis (bad breath).

104
Q

Why is putrescine an unwanted by product?

A

It contributes towards halitosis (bad breath).

105
Q

How much (by weight) of carbohydrates do salivary mucins have?

A

40% (sometimes uptp 80%)

106
Q

What is a consensus sequence ?

A

A sequence which tells the enzymes to add a modification to the amino acid

107
Q

What are oligosaccharides?

A

carbohydrates attached via N- type linkages

108
Q

What are more than one mucin molecules linked together called?

A

Oligomers

IOE Dentistry - Saliva (3 decks)

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