2. PubMed Research Article
“Identification and structural characterization of novel genetic elements in the HIV-1 V3 loop regulation coreceptor usage” by Svicher et al.
Studied the interaction between HIV-1gp120 and CCR5 N terminus

3. HIV-1 entry involves gp120, CD4 recepor and CCR5 or CXCR4
V3 loop is determining factor in coreceptor usage
Composed of 3 regions
Base
Stem
Hairpin crown
V3 positions 11, 24 and 25 bind with different coreceptors but mechanism that differentiates is not know

4. V3 base interaction with CCR5 critical for infection
Increased affinity of V3 for CCR5
Study population: 323 blood samples from 323 HIV-1 patients
V3 mutation was tested for along with wild-type residues to see different coreceptor usage
Structural analysis taken from Huang et al. CCR5 model with HIV-1 gp120

5. V3 sequence determines coreceptor usage
19 V3 sequence positions that correlated to CCR5 of CXCR4 usage
Of 29 mutations, 6 are at the V3 positions of 11, 24 and 25 select for CCR5
23 other mutations at 15 V3 positions select for CXCR4
Mutations for CCR5 not seen in viruses that select for CXCR4 and vice versa
Less that 1% of mutation in each case