Evidence regarding the hypothesis that the histidine–histidine contact pairs may affect protein stability

Role of His-His interaction in Ser474-His475-Tyr476 sequence of chondroitinase ABC I in the enzyme activity and stability

Despite clinical importance of chondroitinase ABC I, its application has been limited due to thermal instability as reported in the literature. There are various approaches to improve thermal stability of enzymes, among them, His-His interactions are believed generally as an effective means. In the present study and for preparing a His-His interaction, various mutations in the sequence of Ser⁴⁷⁴-His⁴⁷⁵-Tyr⁴⁷⁶ at catalytic domain of the enzyme were performed using site directed mutagenesis method. The effect of these mutations on activity, stability and structural features of cABC I was assessed. The study showed that establishment of His475-His476 pair in cABC I, did not improve thermal stability of the enzyme and inactivated it. The study also revealed the existence a hydrogen bond network in the central domain of the enzyme with a specific role for tyrosine 476. In this network, replacement of His⁴⁷⁵ with Ala and Try⁴⁷⁶ with His and Ala, deactivated and destabilized the enzyme; confirming their importance in the enzyme catalysis and stability. Also, it was found that Tyr⁴⁷⁶ has some important role in substrate binding, an issue which should be more investigated.

Marine Microbiological Enzymes: Studies with Multiple Strategies and Prospects

Marine microorganisms produce a series of promising enzymes that have been widely used or are potentially valuable for our daily life. Both classic and newly developed biochemistry technologies have been broadly used to study marine and terrestrial microbiological enzymes. In this brief review, we provide a research update and prospects regarding regulatory mechanisms and related strategies of acyl-homoserine lactones (AHL) lactonase, which is an important but largely unexplored enzyme. We also detail the status and catalytic mechanism of the main types of polysaccharide-degrading enzymes that broadly exist among marine microorganisms but have been poorly explored. In order to facilitate understanding, the regulatory and synthetic biology strategies of terrestrial microorganisms are also mentioned in comparison. We anticipate that this review will provide an outline of multiple strategies for promising marine microbial enzymes and open new avenues for the exploration, engineering and application of various enzymes.

Identification and Structural Analysis of Amino Acid Substitutions that Increase the Stability and Activity of Aspergillus niger Glucose Oxidase

Glucose oxidase is one of the most conspicuous commercial enzymes due to its many different applications in diverse industries such as food, chemical, energy and textile. Among these applications, the most remarkable is the manufacture of glucose biosensors and in particular sensor strips used to measure glucose levels in serum. The generation of ameliorated versions of glucose oxidase is therefore a significant biotechnological objective. We have used a strategy that combined random and rational approaches to isolate uncharacterized mutations of Aspergillus niger glucose oxidase with improved properties. As a result, we have identified two changes that increase significantly the enzyme's thermal stability. One (T554M) generates a sulfur-pi interaction and the other (Q90R/Y509E) introduces a new salt bridge near the interphase of the dimeric protein structure. An additional double substitution (Q124R/L569E) has no significant effect on stability but causes a twofold increase of the enzyme's specific activity. Our results disclose structural motifs of the protein which are critical for its stability. The combination of mutations in the Q90R/Y509E/T554M triple mutant yielded a version of A. niger glucose oxidase with higher stability than those previously described.