Antibody Structure Problem Set

Problem 2. Antibody HV regions

Tutorial to help answer the question

Framework regions, subdivisions of antibody variable regions, are composed of beta sheets with fairly constant amino acids sequences. The variable region of light and heavy chains each have three hypervariable (HV) or complementarity determining regions (CDR) that show dramatic changes in amino acids when antibodies of different specificity are compared. From the exercise, what region of the antibody contacts antigen?

A. framework regions of both light and heavy chains

B. hypervariable regions of the light chain

C. hypervariable regions of the heavy chain

D. hypervariable regions of the light and heavy chains

Tutorial

The yellow and purple structure is the Fab or variable regions of the light and heavy antibody chains. Amino acids that comprise an antibody's HV region form loops (purple) that directly contact the antigen (green). Antibody specificity is determined by the specific amino acid sequence in the HV region of both the light and heavy chains.

This image also illustrates the interactions between the antibody's HV region (purple) and the antigen (green).

In this image, HV regions have been eliminated - only the antibody's FR regions are shown. The antibody's FR regions do not directly contact antigen (green).