The Crystal Structure of a Streptomyces thermoviolaceus Thermophilic Chitinase Known for Its Refolding Efficiency

Analyzing the structure of proteins from extremophiles is a promising way to study the rules governing the protein structure, because such proteins are results of structural and functional optimization under well-defined conditions. Studying the structure of chitinases addresses an interesting aspect of enzymology, because chitin, while being the world’s second most abundant biopolymer, is also a recalcitrant substrate. The crystal structure of a thermostable chitinase from Streptomyces thermoviolaceus (StChi40) has been solved revealing a β/α-barrel (TIM-barrel) fold with an α+β insertion domain. This is the first chitinase structure of the multi-chitinase system of S. thermoviolaceus. The protein is also known to refold efficiently after thermal or chemical denaturation. StChi40 is structurally close to the catalytic domain of psychrophilic chitinase B from Arthrobacter TAD20. Differences are noted in comparison to the previously examined chitinases, particularly in the substrate-binding cleft. A comparison of the thermophilic enzyme with its psychrophilic homologue revealed structural features that could be attributed to StChi40’s thermal stability: compactness of the structure with trimmed surface loops and unique disulfide bridges, one of which is additionally stabilized by S–π interactions with aromatic rings. Uncharacteristically for thermophilic proteins, StChi40 has fewer salt bridges than its mesophilic and psychrophilic homologues.

MATEC Web of Conferences – General and efficient algorithms for handling intricate situations in trimmed surface rendering

Trimmed surfaces have been widely used in complicated product design in mechanical engineering especially in complex free form surface models of CAD/CAM/CAE. Focusing on the deficiencies of the algorithms available in published literatures when handling some intricate situations, this paper proposes a more general and efficient algorithm of trimmed surface rendering (ATSR). The ATSR is a general algorithm that can deal with most intricate situations, which frequently occur in practical engineering that no special attention has been paid to in references at hand, as well as common situations. Furthermore, this paper presents a new algorithm for the nodes of polygon connecting into elements (ANCE). The ANCE can handle most tricky polygons appearing in the process of rendering and achieve successful triangulation for the to-be-rendered surface. Preferable results are obtained in the case studies, which indicate that the algorithms (ATSR and ANCE) are efficient and effective in handling complicated as well as common trimmed surface models in real engineering industry.

Optimization of Process Parameters in CFRP Machining with Diamond Abrasive Cutters

The present paper proposes a methodology to optimize process parameters for trimming applications with diamond abrasive cutters. This methodology is based on the study of quality of trimmed surface, through material integrity and surface roughness, and on the study of cutting mechanisms. Their evolutions according to tool parameters and cutting conditions have been analysed. Results show that diamond grits size must be chosen according to the required surface roughness. Feedrate must respect cutting limitations due to CFRP removal mechanisms with abrasive cutters, which have been identify through analyses of specific cutting energy. Finally, a protocol in two steps is proposed to determine the optimum process parameters according to the application. Firstly, constraint functions due to respect of quality and to limiting cutting phenomena are defined. Thus, limiting values of process parameters are determined. Then, process parameters are selected in order to optimize productivity.