title: Structure at 2.5-A resolution of chemically synthesized human immunodeficiency virus type 1 protease complexed with a hydroxyethylene-based inhibitor.
abstract: The crystal structure of a complex between chemically synthesized human immunodeficiency virus type 1 (HIV-1) protease and an octapeptide inhibitor has been refined to an R factor of 0.138 at 2.5-A resolution. The substrate-based inhibitor, H-Val-Ser-Gln-Asn-Leu psi [CH(OH)CH2]Val-Ile-Val-OH (U-85548e) contains a hydroxyethylene isostere replacement at the scissile bond that is believed to mimic the tetrahedral transition state of the proteolytic reaction. This potent inhibitor has Ki less than 1 nM and was developed as an active-site titrant of the HIV-1 protease. The inhibitor binds in an extended conformation and is involved in beta-sheet interactions with the active-site floor and flaps of the enzyme, which form the substrate/inhibitor cavity. The inhibitor diastereomer has the S configuration at the chiral carbon atom of the hydroxyethylene insert, and the hydroxyl group is within H-bonding distance of the two active-site carboxyl groups in the enzyme dimer. The two subunits of the enzyme are related by a pseudodyad, which superposes them at a 178 degrees rotation. The main difference between the subunits is in the beta turns of the flaps, which have different conformations in the two monomers. The inhibitor has a clear preferred orientation in the active site and the alternative conformation, if any, is a minor one (occupancy of less than 30%). A new model of the enzymatic mechanism is proposed in which the proteolytic reaction is viewed as a one-step process during which the nucleophile (water molecule) and electrophile (an acidic proton) attack the scissile bond in a concerted manner.
authors.affiliation: Macromolecular Structure Laboratory, National Cancer Institute-Frederick Cancer Research and Development Center, Maryland 21702-1201.
authors.forename: M
authors.initials: M
authors.lastname: Jaskólski
authors.forename: A G
authors.initials: AG
authors.lastname: Tomasselli
authors.forename: T K
authors.initials: TK
authors.lastname: Sawyer
authors.forename: D G
authors.initials: DG
authors.lastname: Staples
authors.forename: R L
authors.initials: RL
authors.lastname: Heinrikson
authors.forename: J
authors.initials: J
authors.lastname: Schneider
authors.forename: S B
authors.initials: SB
authors.lastname: Kent
authors.forename: A
authors.initials: A
authors.lastname: Wlodawer
mesh_terms: D000595:Amino Acid Sequence; D005030:Ethylenes; D016333:HIV Protease / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*; D015497:HIV-1 / Q000201:enzymology*; D007202:Indicators and Reagents; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry*; D011480:Protease Inhibitors / Q000138:chemical synthesis / Q000494:pharmacology*; D011487:Protein Conformation; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D005030:Ethylenes; D007202:Indicators and Reagents; D009842:Oligopeptides; D011480:Protease Inhibitors; C067254:hydroxyethylene; D016333:HIV Protease