Hexokinase from the white shrimp Litopenaeus vannamei: cDNA sequence, structural protein model and regulation via HIF-1 in response to hypoxia

Hexokinase (HK) catalyzes the phosphorylation of glucose, the first rate-limiting step in glycolysis. HKs are a conserved family of tissue-specific isozymes, from which very little is known in marine crustaceans. This study describes the cloning and characterization of the full-length cDNA sequence for HK from the shrimp Litopenaeus vannamei, the theoretical tridimensional protein structure and response to short-term hypoxia. The full-length cDNA is 1872bp long with an open reading frame of 1452bp coding for a protein of 484 amino acids and predicted molecular mass of 53kDa. Highly conserved amino acid residues are present in the glucose, glucose-6-phosphate, ATP and Mg(+2) binding sites. Phylogenetic analysis shows that the shrimp HK is closer to invertebrates than to vertebrate HKs. Hypoxia induced HK expression in gills with the concomitant increase in the specific enzyme activity. In muscle, hypoxia decreased HK mRNAs but increased the enzyme activity. Silencing of the hypoxia inducible factor 1 (HIF-1) affected the expression of HK differentially. In gills, silencing of α or β subunits blocked the induction of HK expression and the enzymatic activity, but not in muscle. This suggests the existence of tissue-specific HK isozymes and post-transcriptional and post-translational regulation of HK.