Catalytic efficiency and vitality of HIV-1 proteases from African viral subtypes

Area of Science:

• Virology
• Biochemistry
• Drug Discovery

Background:

• HIV-1 subtypes A and C are prevalent in Africa, unlike the B subtype common in Western countries.
• Genomic variations in HIV-1 subtypes lead to sequence differences in viral proteins, including protease.
• Polymorphisms in HIV-1 protease can influence drug resistance, necessitating subtype-specific efficacy assessments.

Purpose of the Study:

• To enzymatically characterize HIV-1 proteases from drug-naive Ugandan adults representing subtypes A and C.
• To compare the biochemical properties and susceptibility to protease inhibitors of subtype A and C proteases against the subtype B protease.

Main Methods:

• Enzymatic characterization of purified HIV-1 proteases (subtype A, subtype C, and consensus subtype B).
• Determination of catalytic constants (kcat) and Michaelis constants (Km) using various substrates.
• Assessment of inhibition by four protease inhibitors: indinavir, ritonavir, saquinavir, and nelfinavir, by measuring inhibition constants (Ki).

Main Results:

• Subtype A and C proteases exhibited similar catalytic constants (kcat) to subtype B protease.
• Subtype C protease showed a 2.4-fold higher catalytic efficiency than subtype B due to lower Km values.
• Subtype A and C proteases were less effectively inhibited by indinavir, ritonavir, saquinavir, and nelfinavir, with 2.5-7-fold and 2-4.5-fold weaker Ki values, respectively.
• Subtype C protease demonstrated 4-11 times higher vitality, and subtype A protease 1.5-5 times higher vitality than subtype B in the presence of inhibitors.

Conclusions:

• HIV-1 proteases from subtypes A and C possess higher biochemical fitness compared to subtype B.
• The reduced susceptibility of subtype A and C proteases to existing protease inhibitors suggests potential challenges for current antiretroviral therapy in regions where these subtypes are dominant.