PPIA and HIV-1 infection: Here we show that amino acid substitutions at CypA residues A25, K27, P29 and K30, which are proposed to mediate binding at the second site, did not affect the interaction of CypA with self-assembled CA tubes or native viral capsids in vitro nor the function of CypA in HIV-1 infection in HeLa-P4 or Jurkat cells.