title: Identification of protein-protein interfaces by decreased amide proton solvent accessibility.
abstract: Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry was used to identify peptic fragments from protein complexes that retained deuterium under hydrogen exchange conditions due to decreased solvent accessibility at the interface of the complex. Short deuteration times allowed preferential labeling of rapidly exchanging surface amides so that primarily solvent accessibility changes and not conformational changes were detected. A single mass spectrum of the peptic digest mixture was analyzed to determine the deuterium content of all proteolytic fragments of the protein. The protein-protein interface was reliably indicated by those peptides that retained more deuterons in the complex compared with control experiments in which only one protein was present. The method was used to identify the kinase inhibitor [PKI(5-24)] and ATP-binding sites in the cyclic-AMP-dependent protein kinase. Three overlapping peptides identified the ATP-binding site, three overlapping peptides identified the glycine-rich loop, and two peptides identified the PKI(5-24)-binding site. A complex of unknown structure also was analyzed, human alpha-thrombin bound to an 83-aa fragment of human thrombomodulin [TMEGF(4-5)]. Five peptides from thrombin showed significantly decreased solvent accessibility in the complex. Three peptides identified the anion-binding exosite I, confirming ligand competition experiments. Two peptides identified a new region of thrombin near the active site providing a potential mechanism of how thrombomodulin alters thrombin substrate specificity.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0601, USA.
authors.forename: J G
authors.initials: JG
authors.lastname: Mandell
authors.forename: A M
authors.initials: AM
authors.lastname: Falick
authors.forename: E A
authors.initials: EA
authors.lastname: Komives
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000737:chemistry*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D013058:Mass Spectrometry; D051379:Mice; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; C015482:protein kinase modulator; D017868:Cyclic AMP-Dependent Protein Kinases