Proline-Rich Proteins — MFDS Part 1 MCQ
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Correct answer: D — Adsorb to hydroxyapatite and inhibit calcium phosphate crystal growth
The correct answer is D. The molecule described is an acidic salivary proline-rich protein. Its phosphorylated acidic amino-terminal region binds calcium and hydroxyapatite. After adsorption to enamel, it inhibits nucleation and seeded growth of calcium phosphate crystals, helping saliva remain metastably supersaturated while limiting indiscriminate mineral deposition. Option A describes salivary alpha-amylase. Option E is principally mediated by bicarbonate, with phosphate making a smaller contribution to salivary buffering. Option B is primarily a function of mucins and other lubricating glycoproteins. Option C describes the iron-sequestering antimicrobial action of lactoferrin.
Reference: Hay DI, Carlson ER, Schluckebier SK, Moreno EC, Schlesinger DH. Inhibition of calcium phosphate precipitation by human salivary acidic proline-rich proteins: structure-activity relationships. Calcified Tissue International. 1987;40(3):126-132. https://pubmed.ncbi.nlm.nih.gov/3105842/