Question

How do the tertiary and quaternary structures of HIV-1 protease differ ?

Answer 1

Tertiary structure refers to the 3-D arrangement of a protein.
Quaternary structure refers to the arrangement and interactions among constituent subunits of a multimeric protein.

HIV-1 protease is a homodimeric protein. Each subunit is composed of 99 amino acids.
Mutations in HIV-protease make HIV non-infectious.
It is an aspartic protease with Asp-25, Thr-26 and Gly-27 catalytic triad at the active site.
It cleaves newly synthesized polyproteins such as Gag and Gag-pol.

The two polypeptides assemble to form a long tunnel which is covered by two flexible protein flaps.