Protein Structure of a Glycoside Hydrolase Family 30, Subfamily 12 Endo-1,4-β-xylanase.

We have determined the X-ray crystallographic protein structure of endo-1,4-β-xylanase (EX) A from Anaerobacterium chartisolvens (AchXyn30A), a homologue of the recent biochemically characterized glycoside hydrolase family 30, subfamily 12 (GH30_12) EX from Acetivibrio clariflavus (AcXyn30B). The N-terminal GH30 catalytic domains (CDs) of these two enzymes share approximately 63% amino-acid sequence identity and the full-length proteins each consist of the GH30_12 CD, a family 6 carbohydrate-binding module and a C-terminal dockerin domain. In this report, we offer additional support for the recent subfamily classification of these EXs and provide detailed X-ray crystallographic protein structure analysis of AchXyn30A, the first protein structure from this newly defined GH30 subfamily. We also provide comparative structural analysis using a generated AcXyn30B homology model as well as other GH30 subfamily enzymes. Additionally, we examine potential xylan-chain interactions informed by the protein structure. These characterized EXs further illustrate the diversity of xylan-degrading enzymes which have evolved within glycoside hydrolase family 30.