The Location of the Ligand-binding Site of Carbohydrate-binding Modules That Have Evolved from a Common Sequence Is Not Conserved

Mirjam Czjzek, David N. Bolam, Amor Mosbah, Julie Allouch, Carlos Fontes, Luis Ferreira, Olivier Bornet, Véronique Zamboni, Hervé Darbon, Nicola L. Smith, Gary Black, Bernard Henrissat, Harry J. Gilbert

Research output: Contribution to journalArticlepeer-review

95 Citations (Scopus)

Abstract

Polysaccharide-degrading enzymes are generally modular proteins that contain non-catalytic carbohydrate-binding modules (CBMs), which potentiate the activity of the catalytic module. CBMs have been grouped into sequence-based families, and three-dimensional structural data are available for half of these families. Clostridium thermocellum xylanase 11A is a modular enzyme that contains a CBM from family 6 (CBM6), for which no structural data are available. We have determined the crystal structure of this module to a resolution of 2.1 Å. The protein is a β-sandwich that contains two potential ligand-binding clefts designated cleft A and B. The CBM interacts primarily with xylan, and NMR spectroscopy coupled with site-directed mutagenesis identified cleft A, containing Trp-92, Tyr-34, and Asn-120, as the ligand-binding site. The overall fold of CBM6 is similar to proteins in CBM families 4 and 22, although surprisingly the ligand-binding site in CBM4 and CBM22 is equivalent to cleft B in CBM6. These structural data define a superfamily of CBMs, comprising CBM4, CBM6, and CBM22, and demonstrate that, although CBMs have evolved from a relatively small number of ancestors, the structural elements involved in ligand recognition have been assembled at different locations on the ancestral scaffold.
Original languageEnglish
Pages (from-to)48580-48587
JournalThe Journal of Biological Chemistry
Volume276
Issue number51
Publication statusPublished - Dec 2001

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