title: The high resolution crystal structure of the human tumor suppressor maspin reveals a novel conformational switch in the G-helix.
abstract: Maspin is a serpin that acts as a tumor suppressor in a range of human cancers, including tumors of the breast and lung. Maspin is crucial for development, because homozygous loss of the gene is lethal; however, the precise physiological role of the molecule is unclear. To gain insight into the function of human maspin, we have determined its crystal structure in two similar, but non-isomorphous crystal forms, to 2.1- and 2.8-A resolution, respectively. The structure reveals that maspin adopts the native serpin fold in which the reactive center loop is expelled fully from the A beta-sheet, makes minimal contacts with the core of the molecule, and exhibits a high degree of flexibility. A buried salt bridge unique to maspin orthologues causes an unusual bulge in the region around the D and E alpha-helices, an area of the molecule demonstrated in other serpins to be important for cofactor recognition. Strikingly, the structural data reveal that maspin is able to undergo conformational change in and around the G alpha-helix, switching between an open and a closed form. This change dictates the electrostatic character of a putative cofactor binding surface and highlights this region as a likely determinant of maspin function. The high resolution crystal structure of maspin provides a detailed molecular framework to elucidate the mechanism of function of this important tumor suppressor.
authors.affiliation: The Protein Crystallography Unit, Monash Centre for Synchrotron Science and The Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Faculty of Medicine, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Ruby H P
authors.initials: RH
authors.lastname: Law
authors.forename: James A
authors.initials: JA
authors.lastname: Irving
authors.forename: Ashley M
authors.initials: AM
authors.lastname: Buckle
authors.forename: Katya
authors.initials: K
authors.lastname: Ruzyla
authors.forename: Marguerite
authors.initials: M
authors.lastname: Buzza
authors.forename: Tanya A
authors.initials: TA
authors.lastname: Bashtannyk-Puhalovich
authors.forename: Travis C
authors.initials: TC
authors.lastname: Beddoe
authors.forename: Kim
authors.initials: K
authors.lastname: Nguyen
authors.forename: D Margaret
authors.initials: DM
authors.lastname: Worrall
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Bottomley
authors.forename: Phillip I
authors.initials: PI
authors.lastname: Bird
authors.forename: Jamie
authors.initials: J
authors.lastname: Rossjohn
authors.forename: James C
authors.initials: JC
authors.lastname: Whisstock
mesh_terms: D000818:Animals; D001665:Binding Sites; D056668:Cathepsin L; D002403:Cathepsins / Q000737:chemistry; D002645:Chickens; D002942:Circular Dichroism; D018360:Crystallography, X-Ray / Q000379:methods*; D003546:Cysteine Endopeptidases / Q000737:chemistry; D005109:Extracellular Matrix; D016147:Genes, Tumor Suppressor; D006720:Homozygote; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry; D015843:Serpins / Q000737:chemistry*; D013053:Spectrophotometry; D055672:Static Electricity; D013696:Temperature; D014981:Xenopus
chemical_list: D011994:Recombinant Proteins; C085344:SERPIN-B5; D015843:Serpins; D002403:Cathepsins; D003546:Cysteine Endopeptidases; C534281:CTSL protein, human; D056668:Cathepsin L; C534278:Ctsl protein, mouse; C534280:Ctsl protein, rat