Maturation-induced conformational changes of HIV-1 capsid protein and identification of two high affinity sites for cyclophilins in the C-terminal domain

Viral incorporation of cyclophilin A (CS PA) during the assembly of human i mmunodeficiency virus type-1 (HIV-1) is crucial for efficient viral replica tion, CyPA binds to the previously identified Gly-Pro(90) site of the capsi d protein p24, but its role remained unclear. Here we report two new intera ction sites between cyclophilins and p24, Both are located in the C-termina l domain of p24 around Gly-Pro(157) and Gly-Pro(224). Peptides correspondin g to these regions showed higher affinities (K-d similar to 0.3 mu M) for b oth CyPA and cyclophilin B than the best peptide derived from the Gly-Pro(9 0) site (similar to 8 mu M) and thus revealed new sequence motifs flanking Gly-Pro that are important for tight interaction of peptide ligands with cy clophilins. Between CS PA and an immature (unprocessed) form of p24, a K-d of similar to 8 mu M was measured, which corresponded with the K-d of the b est of the Gly-Pro(90) peptides, indicating an association via this site, P rocessing of immature p24 by the viral protease, yielding mature p24, elici ted a conformational change in its C-terminal domain that was signaled by t he covalently attached fluorescence label acrylodan. Consequently, CyPA and cyclophilin B bound with much higher affinities (similar to 0.6 and 0.25 m u M) to the new, i.e. maturation-generated sites. Since this domain is esse ntial for p24 oligomerization and capsid cone formation, CyPA bound to the new sites might impair the regularity of the capsid cone and thus facilitat e in vivo core disassembly after host infection.