The crystal structure of human alpha1-tryptase reveals a blocked substrate-binding region.
Human mast cell tryptases represent a subfamily of trypsin-like serine proteinases implicated in asthma. Unlike beta-tryptases, alpha-tryptases apparently are proteolytically inactive. We have solved the 2.2A crystal structure of mature human alpha1-tryptase. It reveals a frame-like tetrameric architecture that, surprisingly, does not require heparin-binding for stability. In marked contrast to beta2-tryptase, the Ser214-Gly219 segment, which normally provides the template for substrate binding, is kinked in alpha-tryptase, thereby blocking its non-primed subsites. This so far unobserved subsite distortion is incompatible with productive substrate binding and processing. alpha-Tryptase apparently is trapped in this off-conformation by repulsions and attractions of the Asp216 side-chain. However, proteolytic activity could be generated by an induced-fit mechanism.
Marquardt
Ulf
U
Max-Planck-Institut für Biochemie, Abteilung Strukturforschung, Am Klopferspitz 18a, D-82152 Martinsried bei, München, Germany.
Zettl
Frank
F
Huber
Robert
R
Bode
Wolfram
W
Sommerhoff
Christian
C
D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D006801:Humans; D008407:Mast Cells / Q000201:enzymology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases / Q000737:chemistry* / Q000378:metabolism; D013379:Substrate Specificity; D053802:Tryptases
D011994:Recombinant Proteins; D012697:Serine Endopeptidases; D053802:Tryptases