Molecular Analysis Of Cyclic Alpha-Maltosyl-(1 -> 6)-Maltose Binding Protein In The Bacterial Metabolic Pathway

Cyclic alpha-maltosyl-(1 -> 6)-maltose (CMM) is a cyclic glucotetrasaccharide with alternating alpha-1,4 and alpha-1,6 linkages. Here, we report functional and structural analyses on CMM-binding protein (CMMBP), which is a substrate-binding protein (SBP) of an ABC importer system of the bacteria Arthrobacter globiformis. Isothermal titration calorimetry analysis revealed that CMMBP specifically bound to CMM with a K-d value of 9.6 nM. The crystal structure of CMMBP was determined at a resolution of 1.47 angstrom, and a panose molecule was bound in a cleft between two domains. To delineate its structural features, the crystal structure of CMMBP was compared with other SBPs specific for carbohydrates, such as cyclic alpha-nigerosyl-(1 -> 6)-nigerose and cyclodextrins. These results indicate that A. globiformis has a unique metabolic pathway specialized for CMM.