Saliva 3 - Organic components of Saliva

Question 1

What are the organic components of saliva?

Answer 1

Salivary Mucins
Lactoferrin
Statherin
Cyststatins
Immunoglobulins
Proline rich proteins
Histatins
pH rise factors 
Enzymes

Question 2

What are salivary mucins?

Answer 2

Glycosylated proteins (containing between 40- 80 % of carbohydrate on weight basis)
Their function is to protect hard and soft surfaces of the oral cavity
Two types of attachment from sugar to protein(process occurs in ER)
- O linkage (Occurs at Serine & Threonine) most abundant (SOT)
- N linkage (occurs at asparagine) (NA)

Question 3

When do asparagine residue accepts sugars?

Answer 3

An asparagine residue only accepts sugars in a consensus sequence
e.g.
Asn - X - Thr
Asn - X – Ser
Carbohydrates that attach to Asparagine have a common pentasaccharide sequence
Further sugars may be added to this core Sialic acid -ve charge on mucin extended structure for proteins inc. repulsion between chains

Question 4

Describe mucin structure?

Answer 4

Mucins have a carboxyl and an amino end which are rich in cysteine form cross chains with other mucin monomers, linear mucins and mucin oligomers
Central portion rich in serine + threonine saturated with O-linked oligosaccharide

Question 5

What is MG1?

Answer 5

Mucous glycoprotein High molecular weight mix of 3 diff gene products made from many mucin monomers joined by S-S bonding (from cysteine)
Also binds to other salivary proteins (amylase/PRPs)

Question 6

What is MG2?

Answer 6

Binds to bacteria (such as streptococci)

Has a low molecular weight as its one gene product

Question 7

How are MG1&2 expressed?

Answer 7

MG1/MG2 are expressed by different amounts in major/minor glands

Question 8

What are the functions of MG1&2?

Answer 8

Protects oral surface against dryness
MG2 kills bacteria + candida albicans
Lubricates hard and soft tissue
Facilitates speech and swallowing

Question 9

What is the function of lactoferrin?

Answer 9

Binds Fe3+ (iron)
Antibacterial as it depletes area of iron which means bacteria cannot survive without iron
Can be degraded by proteases released by bacteria
Some bacteria (Treponema family) can uptake Lactoferrin and use it for itself

Question 10

What is the function of Statherin?

Answer 10

Prevents against over ppt. of hydroxyapatite mineral (in unwanted places e.g. calculus)
Binds to hydroxyapatite at 2 diff sites & also binds to calcium
Produced via Acinar cells
Asymmetrical distribution of negative charge so amino acid 1-6 bind Ca2+ so no ppt. of HAP
High in proline AA so no alpha helix observed Whole Statherin can also bind to HAP therefore no growth of crystal

Question 11

What is the function of Cystatins?

Answer 11

Small proteins found in the body that binds to proteases to control unwanted protein degradation
Also bind to bacterial proteases and protects hard + soft tissue
Bind to HAP
When fizzy drink consumed it binds to tooth surface (protective)

Question 12

What are the three types of immunoglobulins?

Answer 12

IgG – single Y shaped molecule
IgA – dimer of Y shaped molecules
IgM – Five Y shaped molecules

Y shaped molecule is made from 4 polypeptide chains

Question 13

How does IgA differ to the others?

Answer 13

IgA is main immunoglobulin in saliva secreted by epithelial cells of S. gland
IgA gains additional polypeptide (secretory component) called Sig A (in tears)
This protects it in hostile environments
igA in blood/ tissue fluid doe not contain this secretory component
Immunoglobulins cause Agglutination (easier to be removed)

Question 14

What PRPS?(Proline rich proteins)

Answer 14

Rich in Amino acid proline
Involved in HAP crystal growth and found in pellicle
50% of saliva protein found in submandibular secretion
Secreted by: Trachea & Pharynx
Broken down (proteolytically) in S.glands so there are many PRP’s of diff structures (polymorphic)
High negative charge at amino terminal so binds to Ca2+ mineral inhibit growth
Rest of molecule binds to benign bacterial cell wall to stim growth over harmful bacteria

Statherin, PRP’s and Cystatins play a role in unwanted mineral dep, no role in remineralisation

Question 15

What are Histatins?

Answer 15

Defence peptide found in saliva – Rich in Histidine (also contains Arg & Lys) HAL
Positively charged at physiological pH leads to Basic molecule
pKa of AA are similar to physiological pH act as buffers
Binds calcium stops over ppt. of HAP
Activity against candida & S.Mutans

Question 16

What are pH rise factors?

Answer 16

Urea and Sialin
Sialin 4 AA acid chain (Gly-Gly-Lys-Arg) (go go lucky arj)
Both Urea and sialin used in by bacterial metabolism leads to ammonia release which acts as base
Sialin metabolism causes putriscine release (leads to halitosis)

Question 17

What is enzymes are found in the mouth and what are there roles?

Answer 17

Salivary peroxidase (S.Ps) used tobreak down hydrogen peroxide and thiocyanacte (from food)
SPs – H2O2 + SCN-  OSCN- + H2O

Amylase used to break down dietary carbohydrates

Lysozymes used to break down cell wall in bacteria

Removes toxic reactants to form hypothiocynite powerful antimicrobial

Question 18

How does amylase work?

Answer 18

Amylase break 1-4 glycosidic linkage between glucose ONLY
Varies with flow rate large amount in stimulated saliva
Secreted mostly by the parotid gland
Found in other secretions (tears/bronchial secretion)

Question 19

How do lysozymes work?

Answer 19

Lysozyme (Muramidase) breaks down bacterial cell walls
Hydrolyses N linkage between N-actelymuramic acid and N-acetylglucosamine
Lysozymes also cause agglutination
Act on bacteria that have been ‘tagged’ by sigA
Binds to HAP found in pellicle