Calmodulin-Binding Function of LLP Segments from the HIV Type 1 Transmembrane Protein Is Conserved among Natural Sequence Variants

LLP1 is a peptide, derived from the cytoplasmic tail of HIV-1 TM glycoprotein, that binds and inhibits calmodulin; this region is generally conserved among isolates, but amino acid variation does exist both within clade B and among different clades, as well as SIV, In light of previous studies showing that selected single amino acid changes can have a qualitatively significant effect on the calmodulin-binding properties of this peptide, we sought to examine the properties of naturally occurring variant LLP1 sequences, Using a quantitative fluorescence-based method to measure dissociation constants of calmodulin-LLP1 complexes, a remarkable conservation of calmodulin-binding function among natural variants was revealed, In contrast, engineered nonconservative single amino acid changes altered the affinity of the peptide for calmodulin, The results show that the calmodulin-binding function is well preserved despite the sequence variation observed in nature, suggesting that this region of the TM protein is important to viral replication.