OB S - Salivary pellicle 1 Flashcards
Name some salvia components.
- histatins
- lysozyme
- proline-rich proteins
- amylases
How can protein shape change?
according to conditions
what are the 2 functions of proteolytic cleavage?
1 function as a long molecule but can have another function as a peptide
what does localisation determine ?
what happens i.e can be localised to an area that favours its role
Name some salivary functions.
- Antibacterial i.e amylases/mucins
- Anti-viral i.e cystitis
- Anti-fungal i.e histatins
- Buffering -carbonic anhydrases
what is understanding natural processes linked to?
therapeutic innovations
Describe the formation of a pellicle.
Material deposited rapidly on freshly cleaned tooth:
- Forms in minutes
- 20 mins tooth surface covered
- 120 mins 1-10 μms thick
what does the pellicle contain?
Peptides, proteins, enzymes, glycoproteins, lipids and glycolipids:
- -ve charged enamel surface
- -ve charged salivary proteins
what does the composition and structure of the pellicle vary with?
time and local microenvironment
What is the pellicle?
0.1 - 1.0 μm thick layer of macromolecular material on the mineral surface of teeth
– cell-free proteinaceous layer
– forms rapidly on cleaned tooth surfaces
what are the 3 functions of the pellicle?
• Selective adsorption of hydroxyapatite-reactive salivary
proteins, serum proteins and microbial products – contains most salivary proteins and lipids
• Diffusion barrier
– protects against bacterial acids
– slows loss of dissolved calcium and phosphate ions
• Renewable lubricant, helps protect teeth from attrition and abrasion
what ions does the enamel surface contain?
cations (Ca++) & anions (OH-) (PO4- -)
what is the net charge of the enamel surface?
net -ve charge
what does contact with salvia do to the pellicle?
produces a charged layer :
- hydration layer or stern layer
- counter ions 90% Ca++
- remains while animal is in contact with liquid
what is at high concentration at the tooth surface?
F-
where does pellicle formation occur?
HA discs -dics of hydroxyapatite so the charge varies across the surface
what gives protection of the tooth?
calcium phosphate
what is an impure form of calcium HA?
tooth mineral
what does mass action of calcium phosphate govern?
dissociation
what does loss of calcium phosphate depend on ?
amount of Ca, PO4 & 2OH in
solution
what happens in low pH?
supersaturation decreases
what happens at critical pH?
salvia no longer supersaturated
what happens in high pH (alkaline)?
calcium phosphate can precipitate
what does precipitation require?
nucleation sites
what does the pellicle mask?
the underlying HA crystals from acting as nucleation sites
what can act as a nucleation site?
plaque
Discuss pH:salivary bicarbonate.
- Salivary bicarbonate (HCO3-) stabilised by gaseous CO2
- HCO3- most unstable (high) near salivary ducts
- May result in higher pH can result near duct openings making Calcium Phosphate more likely to precipitate
what is the key function of bicarbonate?
mop up protons and protects the tooth
what is unique to salvia?
carbonic anhydrase IV
what does carbonic anhydrase IV do?
Drives the process pf bicarbonate binding to protons and turning them into water
How does carbonic anhydrase IV act as phase buffering?
– Phase conversion of dissolved CO2 into a volatile gas
– Contributes to neutralising acid
Describe carbonic anhydrase IV.
– Secreted from aciner cells as isoenzyme
– No direct role in buffering saliva
– DMTF index links its concentration to caries
– Binds to pellicle
– Localised protection through removal of H+
what has an affinity for apatitic surfaces suggests it binds before the pellicle formation?
Statherin
what does statherin prevent?
both primary and secondary calcium phosphate disposition
What is statherin and what does it occupy?
• Acidicphosphoprotein
– N-terminal basic residues
– NMR helical structure
– mimics periodicity of acid phosphate clusters on HAp
• Occupies sites that would otherwise be used for nucleating crystallisation?
what does PRPs stand for?
proline-rich proteins
Describe proline-rich proteins.
• Family of proteins – 70% of total salivary protein • Rich in Proline (25-40%), Glutamic acid glutamine & glycine • Amphiphilic – 80% hydrophobic – 20% hydrophilic • 3 groups – acidic (16 kD) – basic (6-9 kD) – glycosylated (36 kD)
what characteristic can proline give a molecule?
flexibility
Describe proteolytic cleavage.
– Oral fluid & glandular
secretions are distinct
– Sterile to non-sterile
– Exposure to bacteria derived proteases.
– Release of peptides derived (in particular) from Acidic & Basic PRPs, Statherin & Histatins.
Describe proline-rich proteins binding to the pellicle.
• Early binding to pellicle, and incorporated into mature
biofilms.
• N-terminus shows structural similarity to Statherin.
• First 30 amino acids negatively charged.
• Proposed to occupy sites where Calcium phosphate deposition would occur
What else can PRPs interact with?
Calcium & phosphate ions away from the HA surface where they may act as ‘sink’ & limit growth of these complexes. Conformational changes may release Calcium & Phosphate ions when required
what are 2 strong inhibitors of calcium phosphate?
– Stratherin
– Acidic Proline-rich proteins
what are 2 moderate inhibitors of calcium phosphate?
– Histatins
– Cystatins
what are 2 weak inhibitors of calcium phosphate?
– Mucins
– Amylase
How is early caries repaired despite presence of mineralization inhibitors in saliva?
- Surface layer of early carious lesion forms impermeable barrier to diffusion of high mol.wt. inhibitors.
- Still permeable to calcium and phosphate ions
- Inhibitors may encourage mineralization by preventing crystal growth on the surface of lesion by keeping pores open
- Inhibitors could form complexes from which Ca2+ & PO4- can be released
what is the most abundant salivary enzyme?
Alpha-amylase
what does alpha -amylase do?
Hydrolyzes α(1-4) glycosidic bonds of polysaccharides;
– Insoluble (large) Starch broken down to soluble starches
– Clears carbohydrate debris on the tooth
what is the major end product of alpha amylase?
maltose
what is alpha amylase resistant to?
proteolytic cleavage
what happens to alpha amylase on the pellicle?
Immobilised on pellicle, in association with mucin &/or antibodies
what does von ebner’s glands of tongue secrete?
lingual lipase
what is lingual lipase involved in?
• Involved in first phase of fat digestion
– i.e. dietary lipids
what does lingual lipase hydrolyse?
Hydrolyzes medium- to long-chain triglycerides
– Diglycerides & free fatty acid are the primary products
what constitutes 90% of acquired pellicle?
salivary glycoproteins :
26% of salivary proteins
what does salivary glycoproteins contain?
acidic sugars (-ve) e.g sialic acid
what are mucin functions?
Tissue Coating
– Protective coating about hard and soft tissues
– Primary role in formation of acquired pellicle
Lubrication
– Align themselves with direction of flow
• (characteristic of asymmetric molecules)
– Increases lubricating qualities
• Film strength determines how effectively opposed moving surfaces are kept apart
what are the two forms of salivary mucins?
- oligomeric mucin glycoprotein (MG1)
- Monomeric mucin glycoprotein (MG2)
Describe oligomeric mucin glycoprotein (MG1).
– Mixture of two mucins (MUC5B & MUC4) >1 x 106 kDa
– Gel-forming mucin (MUC5B) & membrane-bound (MUC4)
– Disulfide linked multimers
– Mucosal & enamel surface coating (major role)
Describe monomeric mucin glycoprotein (MG2).
– One gene product (MUC7) 200-250 kDa
– 170 O & N-linked side chains 68%
– Influence on oral microbiota (major role)
what is the estimated hydrogen peroxide levels in whole salvia?
8-14 uM
what is hydrogen peroxide a major source for?
Facultative anaerobes major source
– e.g. S. sanguinis & S. mitis
what is hydrogen peroxide converted to in mammalian cels?
hydroxyl radicals
-damage DNA and lipids
what is dismutation of hydrogen peroxide critical for?
Protecting mucosa fibroblasts etc:
- bacterial catalases
- salivary peroxidases
Describe salivary peroxidase.
• Sialoperoxidase (hSPO, salivary peroxidase)
– 78 kD
– secreted by the parotid and submandibular glands
– Readily adsorbed to various surfaces of mouth: enamel, salivary sediment, bacteria, dental plaque
what do salivary peroxidase do?
– Oxidise mainly salivary SCN- in the presence of H2O2
– Protect host from H2O2 toxicity
Describe thiocyanate (SCN-).
– Electron donor in reaction
– normal component of saliva
– salivary concentration depends on diet and smoking habits
Thiocyanate reactions .
look at slide
