The crystal structure of the complex between human immunodeficiency virus type 1 (HIV-1) protease and a peptidomimetic inhibitor of ethyleneamine type has been refined toRfactor of with diffraction limit A ˚ .The peptidomimetic inhibitor Boc-Phe-Y[CH2CH2 NH]-Phe-Glu-Phe-NH2 (denoted here as OE) contains the ethylene-amine replacement of the scissilepeptidebond. The inhibitor lacks the hydroxyl group which is believed to mimic tetra-hedral transition state of proteolytic reaction and thus is suspected to be necessary for good properties of peptido-mimetic HIV-1 protease inhibitors
