title: Curling of flap tips in HIV-1 protease as a mechanism for substrate entry and tolerance of drug resistance.
abstract: BACKGROUND
  The human immunodeficiency virus type 1 (HIV-1) protease is an essential viral protein that is a major drug target in the fight against Acquired Immune Deficiency Syndrome (AIDS). Access to the active site of this homodimeric enzyme is gained when two large flaps, one from each monomer, open. The flap movements are therefore central to the function of the enzyme, yet determining how these flaps move at an atomic level has not been experimentally possible.
  
  
  RESULTS
  In the present study, we observe the flaps of HIV-1 protease completely opening during a 10 ns solvated molecular dynamics simulation starting from the unliganded crystal structure. This movement is on the time scale observed by Nuclear Magnetic Resonance (NMR) relaxation data. The highly flexible tips of the flaps, with the sequence Gly-Gly-Ile-Gly-Gly, are seen curling back into the protein and thereby burying many hydrophobic residues.
  
  
  CONCLUSIONS
  This curled-in conformational change has never been previously described. Previous models of this movement, with the flaps as rigid levers, are not consistent with the experimental data. The residues that participate in this hydrophobic cluster as a result of the conformational change are highly sensitive to mutation and often contribute to drug resistance when they do change. However, several of these residues are not part of the active site cavity, and their essential role in causing drug resistance could possibly be rationalized if this conformational change actually occurs. Trapping HIV-1 protease in this inactive conformation would provide a unique opportunity for future drug design.
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester 01655, USA.
authors.forename: W R
authors.initials: WR
authors.lastname: Scott
authors.forename: C A
authors.initials: CA
authors.lastname: Schiffer
mesh_terms: D001665:Binding Sites / Q000235:genetics; D003198:Computer Simulation; D017124:Conserved Sequence; D004352:Drug Resistance, Microbial / Q000235:genetics; D005998:Glycine / Q000235:genetics; D016333:HIV Protease / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015497:HIV-1 / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D006801:Humans; D007532:Isoleucine / Q000235:genetics; D008024:Ligands; D008715:Methionine / Q000235:genetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010649:Phenylalanine / Q000235:genetics; D011487:Protein Conformation; D012997:Solvents; D055672:Static Electricity; D013379:Substrate Specificity / Q000235:genetics; D013816:Thermodynamics
chemical_list: D008024:Ligands; D010446:Peptide Fragments; D012997:Solvents; D007532:Isoleucine; D010649:Phenylalanine; D008715:Methionine; D016333:HIV Protease; D005998:Glycine