Structural insight into substrate specificity of human intestinal maltase-glucoamylase

Human maltase-glucoamylase(MGAM)hydrolyzes linear alpha-1,4-linked oligosaccharide substrates,playing a crucial role in the production of glucose in the human lumen and acting as an efficient drug target for type 2 diabetes and obesity.The amino-and carboxyl-terminal portions of MGAM(MGAM-N and MGAM-C)carry out the same catalytic reaction but have different substrate specificities.In this study,we report crystal structures of MGAM-C alone at a resolution of 3.1Å,and in complex with its inhibitor acarbose at a resolution of 2.9Å.Structural studies,combined with biochemical analysis,revealed that a segment of 21 amino acids in the active site of MGAM-C forms additional sugar subsites(+2 and+3 subsites),accounting for the preference for longer substrates of MAGM-C compared with that of MGAM-N.Moreover,we discovered that a single mutation of Trp1251 to tyrosine in MGAM-C imparts a novel catalytic ability to digest branched alpha-1,6-linked oligosaccharides.These results provide important information for understanding the substrate specificity of alphaglucosidases during the process of terminal starch digestion,and for designing more efficient drugs to control type 2 diabetes or obesity.

Crystallographic studies on the binding of coenzyme analogs to D-glyceraldehyde-3-phosphate dehydrogenase from Palinurus versicolor

In contrast with the coezyme, two coenzyme analogs, ADP-ribose and SNAD, bind non-cooperatively to D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Palinurus versicolor (PV) GAPDH complexed with ADP-ribose and SNAD has been crystallized by the method of sitting-drop vapor diffusion. X-ray diffraction data analysis reveals that both crystals belong to the same space group (C2), and have similar cell dimensions: a =152.80 A, b =100.35 A, c =128.31 A, β=110.28° and a =153.41 A, b =100.51 A, c =128.44 A, β =110.48°, respectively. It is estimated that the asymmetric unit in each crystal contains 4 subunits. This is a novel crystal form which is quite different from that previously reported for holo- and apo-GAPDH from the same spurce. The result suggests that the binding of the two coenzyme analogs to GAPDH may lead to some significant conformational changes, which are different from those induced by the coenzyme binding. The self-rotation function indicates that the tetramer of these two GAPDH

Crystal structures of catalytic core domain of BIV integrase: implications for the interaction between integrase and target DNA

Integrase plays a critical role in the recombination of viral DNA into the host genome.Therefore,over the past decade,it has been a hot target of drug design in the fight against type 1 human immunodeficiency virus(HIV-1).Bovine immunodeficiency virus(BIV)integrase has the same function as HIV-1 integrase.We have determined crystal structures of the BIV integrase catalytic core domain(CCD)in two different crystal forms at a resolution of 2.45Åand 2.2Å,respectively.In crystal form I,BIV integrase CCD forms a back-to-back dimer,in which the two active sites are on opposite sides.This has also been seen in many of the CCD structures of HIV-1 integrase that were determined previously.However,in crystal form II,BIV integrase CCD forms a novel face-toface dimer in which the two active sites are close to each other.Strikingly,the distance separating the two active sites is approximately 20Å,a distance that perfectly matches a 5-base pair interval.Based on these data,we propose a model for the interaction of integrase with its target DNA,which is also supported by many published biochemical data.Our results provide important clues for designing new inhibitors against HIV-1.

The structure of WbnH in a near active state

Dear Editor, Gram-negative bacteria possess a complicated membrane system that plays an essential role in interactions between bacteria and the envJronment （Reeves and Wang, 2002）. The inner leaflet of the membrane is composed of various glycerophospholipids, and the outer leaflet consists primarily of lipopolysaccharide （LPS） molecules.