Alkaline unfolding and salt-induced folding of arginine kinase from shrimp Feneropenaeus chinensis under high pH conditions

Genomic structure, expression and functional characterization of arginine kinase (EcAK) from Exopalaemon carinicauda

Arginine kinase (AK, EC 2.7.3.3) plays an important role in cells with high, fluctuating energy requirements. In invertebrates, AK is the major phosphagen kinase that modulates the energy metabolism. Here, the full-length cDNA sequence encoding arginine kinase (EcAK) was obtained from the Exopalaemon carinicauda. The complete nucleotide sequence of EcAK contained a 1068 bp open reading frame (ORF) encoding EcAK precursor of 355 amino acids. The genomic DNA fragment of EcAK with the corresponding cDNA sequence is composed of 4 exons and 3 introns. The domain architecture of the deduced EcAK protein contained an ATP-gua_PtransN domain and an ATP-gua_Ptrans domain. EcAK mRNA was predominantly expressed in the muscle. The expression of EcAK in the prawns challenged with Vibrio parahaemolyticus and Aeromonas hydrophila changed in a time-dependent manner. Then, EcAK was recombinantly expressed in Pichia pastoris and the purified recombinant EcAK had the same enzymatic characterization as AK from the muscle of Euphausia superba. In conclusion, EcAK may play the same biological activity in E. carinicauda as those from other crustaceans.

Analysis, characterisation and expression of gill-expressed carbonic anhydrase genes in the freshwater crayfish Cherax quadricarinatus

Changes in water quality parameters such as pH and salinity can have a significant effect on productivity of aquaculture species. Similarly, relative osmotic pressure influences various physiological processes and regulates expression of a number of osmoregulatory genes. Among those, carbonic anhydrase (CA) plays a key role in systemic acid-base balance and ion regulation. Redclaw crayfish (Cherax quadricarinatus) are unique in their ability to thrive in environments with naturally varied pH levels, suggesting unique adaptation to pH stress. To date, however, no studies have focused on identification and characterisation of CA or other osmoregulatory genes in C. quadricarinatus. Here, we analysed the redclaw gill transcriptome and characterized CA genes along with a number of other key osmoregulatory genes that were identified in the transcriptome. We also examined patterns of gene expression of these CA genes when exposed to three pH treatments. In total, 72,382,710 paired end Illumina reads were assembled into 36,128 contigs with an average length of 800bp. Approximately 37% of contigs received significant BLAST hits and 22% were assigned gene ontology terms. Three full length CA isoforms; cytoplasmic CA (ChqCAc), glycosyl-phosphatidylinositol-linked CA (ChqCAg), and β-CA (ChqCA-beta) as well as two partial CA gene sequences were identified. Both partial CA genes showed high similarity to ChqCAg and appeared to be duplicated from the ChqCAg. Full length coding sequences of Na(+)/K(+)-ATPase, V-type H(+)-ATPase, sarcoplasmic Ca(+)-ATPase, arginine kinase, calreticulin and Cl(-) channel protein 2 were also identified. Only the ChqCAc gene showed significant differences in expression across the three pH treatments. These data provide valuable information on the gill expressed CA genes and their expression patterns in freshwater crayfish. Overall our data suggest an important role for the ChqCAc gene in response to changes in pH and in systemic acid-base balance in freshwater crayfish.

Cloning and expression of arginine kinase from a swimming crab, Portunus trituberculatus

Arginine kinase (AK) is an important phosphotransferase that plays a critical role in energy metabolism in invertebrates. In this paper, the cDNA of AK (designated as PtAK) was identified from the eyestalk cDNA library of swimming crab Portunus trituberculatus. The full-length cDNA was 1,479 bp, containing an open reading frame of 1,074 bp that coded for 357 amino acids. The estimated molecular mass of mature PtAK was 40.30 kDa and theoretical isoelectric point was 6.18. Amino acid sequence alignment showed that PtAK had very high similarity with other shrimp and crab AKs ranging from 0.876 to 0.983. The genomic DNA fragments of about 1,434 bp consisted of two exons interrupted by an intron. Totally 24 SNPs, including 17 in the coding region and seven in the non-coding region, were detected by direct sequencing of 19 genomic samples. In exon 1, the coding SNPs (cSNPs) were only found in the disease-resistant specimens. The fluorescent real-time PCR analysis revealed that the expression of PtAK was detected in all the examined tissues with the highest expression in the muscle and the lowest in the eyestalk. The expression of PtAK after Vibrio alginolyticus injection was tested in haemocytes, showing that two peak values were 5.01-fold (at 3 h) and 3.60-fold (at 24 h) compared with the control values, respectively. The results suggested that AK might play an important role in the immune response in crabs.

Metal-Binding Properties of a Dicysteine-Containing Motif in Protein Tyrosine Kinases

Studying the structural consequences of the direct binding of arsenite, cadmium, cobalt, nickel, and lead to a number of protein tyrosine kinases led to the discovery of the metal-binding properties of a dicysteine-containing motif in the C-terminal (CT) lobe of the kinases. Of all the synthesized peptides derived from different domains of c-Src and Csk, only peptides based on a dicysteine-containing motif located in the CT lobe of the kinase domain-CPESLHDLMCQC and CPESLHDLMC in c-Src, and CPPAVYDVMKNC in Csk-exhibited significant conformational changes in the presence of all metals, as shown by circular dichroism (CD) analyses. Furthermore, CD analysis of natural enzymes c-Src, Csk, Fyn, c-Abl, Lck, EGFR, and c-Src domains containing the CT lobe in the presence of metals showed a significant concentration-dependent conformational change. ICP-MS, (113)Cd NMR, (33)S NMR, and/or molecular modeling studies of CPESLHDLMC and CPPAVYDVMKNC confirmed the binding between the free sulfhydryl groups of the cysteine residues and Cd(II) or As(III). UV-titration studies suggested a high-affinity interaction between Cd(II) and As(III) and the peptides (K(d) values in the range of 0.6-18.3 nM).