No abstract

Yaks are a multifunctional and dominant livestock species on the Qinghai-Tibetan plateau. The yak grazing system is a traditional transhumance system. Research is focussed on both understanding and improving the system. Development of local economies and the use of new knowledge from yak research and modern technology are improving the system. However, the Qinghai-Tibetan plateau ecosystem is becoming dysfunctional through adverse climate sequences, over-population and over-grazing. The Chinese Government has implemented regional projects to address these degradation problems. Several policies have recently been introduced to improve yak grazing management. This paper reviews current knowledge on the system and the options for improving and optimising the system.

Implementation of a non-natural cofactor alternative to the ubiquitous redox cofactor nicotinamide adenosine dinucleotide (NAD) is of great scientific and biotechnological interest. Several redox enzymes have been engineered to favor nicotinamide cytosine dinucleotide (NCD), a smaller-sized NAD analogue. However, molecular interactions involving NAD analogues remain elusive, preventing us from devising more enzymes to accept those analogues. Here we took a semirational approach to evolve phosphite dehydrogenase (Pdh) and identified variants with substantially improved NCD preference. These mutants are valuable components for regeneration of reduced NCD by using phosphite as the electron donor. We then collected X-ray crystal structures of three Pdh variants and their NCD-complexes to delineate molecular basis for NCD binding. It was found that the incorporation of amino acid residues with large side chains enclosing the NAD-binding pocket led to compacted environment favoring NCD over NAD, and additional interactions between NCD and these side chains. These results guided successful engineering of more Pdh mutants with good NCD preference. As many redox enzymes share key structural features, our strategy may be readily adopted to devise NCD-favoring enzymes. We expected that, in the near future, more synthetic systems linked to non-natural cofactors will be created as alternative tools for widespread applications to address challenging problems by chemical and synthetic biologists.