Maltodextrin-binding proteins from diverse bacteria and archaea are potent solubility enhancers.

Escherichia coli maltose-binding protein (MBP) is frequently used as an affinity tag to facilitate the purification of recombinant proteins. An important additional attribute of MBP is its remarkable ability to enhance the solubility of its fusion partners. MBPs are present in a wide variety of microorganisms including both mesophilic and thermophilic bacteria and archaea. In the present study, we compared the ability of MBPs from six diverse microorganisms (E. coli, Pyrococcus furiosus, Thermococcus litoralis, Vibrio cholerae, Thermotoga maritima, and Yersinia pestis) to promote the solubility of eight different aggregation-prone proteins in E. coli. In contrast to glutathione S-transferase (GST), all of these MBPs proved to be effective solubility enhancers and some of them were even more potent solubilizing agents than E. coli MBP.

Differential effects of short affinity tags on the crystallization of Pyrococcus furiosus maltodextrin-binding protein.

Pyrococcus furiosus maltodextrin-binding protein readily forms large orthorhombic crystals that diffract to high resolution. This protein was used as a model system to investigate the influence of five short affinity tags (His(6), Arg(5), Strep tag II, FLAG tag and the biotin acceptor peptide) on the formation of protein crystals and their ability to diffract X-rays. The results indicate that the amino-acid sequence of the tag can have a profound effect on both of these parameters. Consequently, the ability to obtain diffracting crystals of a particular protein may depend as much on which affinity tag is selected as it does on whether an affinity tag is used at all.

Residues 207, 216, and 221 and the catalytic activity of mGSTA1-1 and mGSTA2-2 toward benzo[a]pyrene-(7R,8S)-diol-(9S,10R)-epoxide.

Murine class alpha glutathione S-transferase subunit types A2 (mGSTA2-2) and A1 (mGSTA1-1) have high catalytic efficiency for glutathione (GSH) conjugation of the ultimate carcinogenic metabolite of benzo[a]pyrene, (+)-anti-7,8-dihydroxy-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene, [(+)-anti-BPDE]. Only 10 residues differ between the sequences of mGSTA1-1 and 2-2. However, the catalytic efficiency of mGSTA1-1 for GSH conjugation of (+)-anti-BPDE is >3-fold higher as compared with mGSTA2-2. The crystal structure of mGSTA1-1 in complex with the GSH conjugate of (+)-anti-7,8-dihydroxy-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (GSBpd) reveals that R216 and I221 in the last helix play important roles in catalysis [Gu, Y., Singh, S. V., and Ji, X. (2000) Biochemistry 39, 12552-12557]. The crystal structure of mGSTA2-2 in complex with GSBpd has been determined, which reveals a different binding mode of GSBpd. Comparison of the two structures suggests that residues 207 and 221 are responsible for the different binding mode of GSBpd and therefore contribute to the distinct catalytic efficiency of the two isozymes.