title: The accessory domain changes the accessibility and molecular topography of the catalytic interface in monomeric GH39 β-xylosidases.
abstract: β-Xylosidases (EC 3.2.1.37) are among the principal glycosyl hydrolases involved in the breakdown of hemicelluloses, catalyzing the reduction of xylooligosaccharides to free xylose. All GH39 β-xylosidases structurally characterized to date display a modular multi-domain organization that assembles a tetrameric quaternary structure. In this work, the crystal structure and the SAXS molecular envelope of a new GH39 β-xylosidase from Caulobacter crescentus (CcXynB2) have been determined. Interestingly, CcXynB2 is a monomer in solution and comparative structural analyses suggest that the shortened C-terminus prevents the formation of a stable tetramer. Moreover, CcXynB2 has a longer loop from the auxiliary domain (the long α-helix-containing loop) which makes a number of polar and hydrophobic contacts with the parental (α/β)(8)-barrel domain, modifying the accessibility and the molecular topography of the catalytic interface. These interactions also maintain the accessory domain tightly linked to the catalytic core, which may be important for enzyme function and stability.
authors.affiliation: Laboratório Nacional de Biociências (LNBio), Centro Nacional de Pesquisa em Energia e Materiais, Rua Giuseppe Maximo Scolfaro, 10000, Campinas-SP 13083-970, Brazil.
authors.forename: Camila Ramos
authors.initials: CR
authors.lastname: Santos
authors.forename: Carla Cristina
authors.initials: CC
authors.lastname: Polo
authors.forename: Juliana Moço
authors.initials: JM
authors.lastname: Corrêa
authors.forename: Rita de Cássia Garcia
authors.initials: Rde C
authors.lastname: Simão
authors.forename: Flavio Augusto Vicente
authors.initials: FA
authors.lastname: Seixas
authors.forename: Mario Tyago
authors.initials: MT
authors.lastname: Murakami
mesh_terms: D020816:Amino Acid Motifs; D020134:Catalytic Domain; D016935:Caulobacter crescentus / Q000201:enzymology*; D018360:Crystallography, X-Ray; D056004:Molecular Dynamics Simulation; D025941:Protein Interaction Mapping; D017433:Protein Structure, Secondary; D053838:Scattering, Small Angle; D014961:X-Ray Diffraction; D014995:Xylosidases / Q000737:chemistry*
chemical_list: D014995:Xylosidases; C026579:exo-1,4-beta-D-xylosidase