Gag^p17 protein KSKK→KSQQ substitution and ΔKSKK deletion mutations promote HIV-1 release and Gag^p17 maturation in HIV-1 CRF55_01B and CRF59_01B strains

To investigate the molecular mechanisms driving rapid spread of HIV-1 CRF59_01B and CRF55_01B among men who have sex with men (MSM) in China and the molecular evolution and dispersal pathways of ΔKSKK deletion and KSKK→KSQQ substitution mutations in HIV-1 Gag^p17 protein.

The characteristic mutations of Gag^p17 protein in the CRF59_01B and CRF55_01B strains were analyzed. HIV-1 mutant plasmids carrying the ΔKSKK deletion mutation and KSKK→KSQQ substitution mutation were constructed and their effects on viral release and maturation were evaluated. Spatiotemporal diffusion maps and key transmission chains of the two mutations were reconstructed using Bayesian discrete phylogeographic analysis.

Compared with HIV-1 subtype B, 9 out of 10 CRF59_01B strains carried a deletion mutation of amino acids 110-113 (ΔKSKK deletion) in the Gag^p17 protein, while 23 out of 29 CRF55_01B strains had a KSKK→KSQQ mutation. Compared with the wild-type virus, the ΔKSKK deletion and KSKK→KSQQ substitution mutants showed increased Gag^p24 protein levels in cell culture supernatants by 173% and 99%, increased viral release efficiency to 161% and 152%, and enhanced Gag protein cleavage efficiency by 47% and 64%, respectively, with also increased proportions of viruses with a typical cone-shaped core (from 18% to 25%-27%). Molecular evolutionary analysis suggested that the ΔKSKK deletion mutation originated in southern Africa around 1938 (P=0.832), then spread to Asia with Australia as the intercontinental hub and China as a "bridge" in the transmission chain; The KSKK→KSQQ substitution mutation originated in Zambia around 1929 (P=0.918) and spread to China, then to the Americas, Europe, and Asia with Thailand and Australia as transmission hubs.

The KSKK→KSQQ substitution and ΔKSKK deletion mutations in Gag^p17 protein characteristic of HIV-1 CRF55_01B and CRF59_01B strains result in enhanced viral replication and infectivity by modulating HIV-1 viral release and Gag protein cleavage maturation.