title: The active site of pepsin is formed in the intermediate conformation dominant at mildly acidic pH.
abstract: Pepsin is an aspartic protease that acts in food digestion in the mammal stomach. An optimal pH of around 2 allows pepsin to operate in its natural acidic environment, while at neutral pH the protein is denatured. Although the pH dependence of pepsin activity has been widely investigated since the 40s, a renewed interest in this protein has been fueled by its homology to the HIV and other aspartic proteases. Recently, an inactive pepsin conformation has been identified that accumulates at mildly acidic pH, whose structure and properties are largely unknown. In this paper, we analyse the conformation of pepsin at different pHs by a combination of spectroscopic techniques, and obtain a detailed characterisation of the intermediate. Our analysis indicates that it is the dominant conformation from pH 4 to 6.5. Interestingly, its near UV circular dichroism spectrum is identical to that of the native conformation that appears at lower pH values. In addition, we show that the intermediate binds the active site inhibitor pepstatin with a strength similar to that of the native conformation. Pepsin thus adopts, in the 6.5-4.0 pH interval, a native-like although catalytically inactive conformation. The possible role of this intermediate during pepsin transportation to the stomach lumen is discussed.
authors.affiliation: Departamento de Bioquímica y Biología Molecular y Celular and Biocomputation and Complex Systems Physics Institute, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza, Spain.
authors.forename: Luis Alberto
authors.initials: LA
authors.lastname: Campos
authors.forename: Javier
authors.initials: J
authors.lastname: Sancho
mesh_terms: D001665:Binding Sites; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D010434:Pepsin A / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet
chemical_list: D010434:Pepsin A