organic components of saliva Flashcards
total salivary protein content
1-6g/L
Proteins can be categorised according to function:
-protein with lubricating properties
-protein with antimicrobial properties
-mineral binding properties
What are mucins
high molecular weight glycoproteins which connected by O and N linked sugars
How much of proteins are mucins?
-over 25% salivary proteins are mucins
-lubricant properties of salivary glycoproteins is directly related to their structure
How are carbohydrates added?
-carbohydrates are added to proteins by covalent attachment to amino acid side chains
-N and O linkage. Occurs after polypeptide chain has been synthesised via specialised enzymes in endoplasmic reticulum and Golgi. E.g. of protein post-translational modification
-both O and N linked sugars are found in salivary mucin but O linkages are most abundant
-O linked sugars are added to serine (SDDR) or threonine THR amino acid residues within mucin polypeptide chains via side chains which both terminate with hydroxyl group
-Glycosidic type of O linkage
-N linked sugars are attached to the amide nitrogen of the side chain of asparagine ASN within polypeptide chain
-carbohydrate only added to asparagine side chains where the asparagine occurs as part of the sequence asparagine, other amino acid threonine/serine
-sequence which tells the enzymes to add a modification to amino acid a consensus sequence
What is stricture of N-linked oligosaccharides?
all have 3 mannose and 2 N-acetylglucosamine residues to which further sugars are attached
–further sugars are then attached to common core
-sialic acid is frequently part of oligosaccharide structure in salivary mucins
Charge of salivary mucins
-presence of substituted carb such as sialic acid confers a negative charge on salivary mucins and results in extended structure for proteins in solution due to repulsion of charges
Structure of mucin monomer
-carboxyl and amino terminal domains rich in cystine residues, make covelant cross links through sulphur side chain
-this way more than one of these monomeric structures can be linked in linear fashion to form mucin oligomers
-central proton formed of multiple repeats of 10-80 amino acid residue sequences, in which 1/2 of amino acids are serine or threonine
-becomes saturated with 100s of O linked oligosaccharides
-N linked oligosaccharides also found on mucins but less abundalntly
2 types of salivary muffins
MG1 and MG2
- MG1=high molecular weight mucin 1MDa
-low molecular weight mucin=MG2 250kDA
-MG=mucous glycoprotein
-MG1 is mixture of 3 diff gene products, MG2 is single gene
-MG2 binds to pathogens and yeast
-MG1 binds to salivary components amylase, PRPs, statherin, histatins
function of salivary muffins
-protection for oral surfaces
-lubrication of soft and hard tissues
-barrier to microbial colonisation
-anti microbial activity
-
statherin
-high proline content
-small size 5kDa
-binds to HAP
-inhibition of crystal
proline rich proteins
50mg/100ml
-high -ve charge
-strongly adsorbed to HAP
-inhibits HAP growth
-highly selective, exclusion of pathogens
histatins
rich in HIS
-at ph 6 -1/2 side chains will be protonated, 1/2 will be neutral
-at least 6 histatins present in saliva
-also found in pellicle proteins at tooth surface
-3kDa
-bind to HAP
-3mg/100ml
-function is buffer and inhibitor of Candida albicans
immunoglobulins
-aid defence of pathogens
-igA-secreted via gland epithelium
-igM-from GFC
-igG- from GFC
-bacterial agglutination
enzymes
amylase and lysosome and salivary peroxidase
