properties of salivary proteins
- lubricating properties
- anti-microbial
- mineral binding properties
role of salivary mucins
- oral lubrication
- facilitates speech and swallowing
- bacterial agglutination
- direction of bacterial attachement
- barrier to demineralisation
- protects hard and soft tissue from damage
how are carbs added to the proteins
by covalent attachments to the amino acid side chain
two types of covalent bonds that form
N linkages and O linkages
which linkage is more abundant in salivary mucins
- o linkages
o linked sugars are added to
serine amino acid residues
and
Thronine amino acid residues
n linked sugars are added to
amide nitrogen of side chain of the asparginie
When do asparagine residue accepts sugars?
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
n linked oligaosaccharides- common structure
3 mannose and 2 n acetylglucosamine residues- to which further sugars can be attached
describe mucin structure
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
oligomers
similar to polymers but with far less repeating units
two types of salivary mucins
MG1 and MG2
MG1
- high molecular weight
- mixture of 3 different gene products
- larger than MG2
- oligemeric strucutre
- made from many mucin monomers joined by S-S bonding (from cysteine)
- Also binds to other salivary proteins (amylase/PRPs)
MG2
- dervies from 1 single gene
- single monomer
- lower molecular weigh that MG1
- binds to oral pathogens and yeast
- purified MG2 can kill oral bacteria
statherin
- important component of salivary pellicle
- unique amino acid primary sequence-high proline content
- small molecular weight
- high negative charge
statherin produced by
acinar cells
function of statherin
inhibition of spontaneous precipitation of hydroxypaetite
- inhibition of crystal/secondary growth of hydroxyapetite
explanation of function of statherin
Saliva is supersaturated with respect to HAP at neutral pH – this is essential for tooth remineralization and inhibition of demineralisation. However, this concentration of mineral ions in saliva could lead to the unwanted deposition of mineral, if left uncontrolled.
Calculus can build up, leading to periodontal disease and stones can then block the salivary gland ducts.
Therefore, statherin binds to HAP and inhibits its growth.
It also binds to calcium and prevents the spontaneous precipition of HAP, reducing the possibility of the formation of calculus/tartar.
primary structure of statherin
- very asymmetric strucutre
-asymmetric distribution of negative charge
high poline content - binds to HAP and inhibits further crystal growth
PRPs
- important component of salivary pellicle
-rich in submandibular secretions
makes up almost half of the total salivary proteins
-polymorphic - derived from genes on chromosome 12
-acidic
imino acid
- secondary amino acid
- has a SECOND amine group
- contains both C=NH and c=o functional groups
function of PRPs
- role in controlling/inhibiting mineral crystal group- strongly adsorbed to HAP
- interact with oral MO- COOH terminal interacts with bacterial cell walls
- highly selective- exclusion of pathogen from the dental surfaces bu binding to the mineral and interacting with BENIGN MO - favour their colonisation over pathogens
histatines
- small defense peptides
-rich in histadine - side chain- imidazole ring
- basic proteins at physiological pH
- conc in saliva is relatively low
- inhibitor of candida
- activity against streptococcus mucans
histatin-1 binds calcium and prevents HAP precipitation
-highly conserved
how many lcasses of immunoglobbins are present in saliva
3
- imG, igG and igA
