Q.24 The polymorphic domains for Class II MHC proteins are
- (A) α1 and β2 domains only
- (B) β1 and α2 domains only
- (C) α1 domains only
- (D) α2 and β2 domains only
The polymorphic domains for Class II MHC proteins are β1 and α2 domains only. This SEO-optimized article answers the MCQ: The polymorphic domains for Class II MHC proteins are (A) α1 and β2 domains only, (B) β1 and α2 domains only, (C) α1 domains only, (D) α2 and β2 domains only—essential for immunology, molecular biology, and biotechnology students studying antigen presentation.
Correct Answer: Option (B) β1 and α2 Domains Only
Class II MHC molecules (HLA-DR/DP/DQ) consist of α and β chains, each with two extracellular domains: α1/α2 and β1/β2. The peptide-binding groove forms from membrane-distal α1 and β1 domains, while α2 and β2 are membrane-proximal Ig-like domains.
Polymorphism (genetic variation creating peptide specificity) occurs primarily in β1 domains (contact peptide side chains) and α2 domains (support groove structure). α1 and β2 show minimal variation as they form conserved peptide backbone contacts.
Explanation of All Options
MHC II polymorphism enables diverse peptide presentation to CD4+ T cells:
-
(A) α1 and β2 domains only: Incorrect. α1 conserved; β2 Ig-like domain minimally polymorphic.
-
(B) β1 and α2 domains only: Correct. β1 pocket residues polymorphic; α2 supports variable groove architecture.
-
(C) α1 domains only: Incorrect. α1 highly conserved across alleles for universal peptide backbone binding.
-
(D) α2 and β2 domains only: Incorrect. β2 minimally variable; both Ig-domains less polymorphic than peptide-contact regions.
Option Domains Polymorphic? Function Correct/Incorrect (A) α1, β2 Backbone binding, Ig-support Low Structural scaffold Incorrect (B) β1, α2 Peptide pockets, groove High Allele specificity Correct (C) α1 only Backbone binding Low Conserved contacts Incorrect (D) α2, β2 Groove support, Ig Moderate Secondary variation Incorrect Biotechnology Relevance
Polymorphic β1 domains determine vaccine efficacy (peptide-MHC binding prediction), links to your N-glycosylation (Q.13) and translation inhibition (Q.23) research for designing MHC-compatible recombinant antigens. HLA typing via β1 sequencing guides personalized immunotherapy.
-
