[Construction of the mutants of rice nonspecific lipid transfer protein and expression comparison in two kinds of thioredoxin fusion expression vectors].

Five structural important residues of rice nonspecific lipid transfer protein LTP110 were mutated by site-directed mutagenesis. Sequence results showed that they were all mutated successfully. After trying various E. coli expression systems, thioredoxin fusion expression system was found to be a proper system to express wild type and mutant LTP110. cDNA sequences encoding wild type LTP110 and the mutants Y17A, P72L, R46A, D43A, C50A were cloned into two kinds of thioredoxin fusion expression vectors. The expression results were compared. In pTrxFus/GI724 expression system, wild type LTP110 and the mutants Y17A, P72L, R46A could be expressed at low level while D43A and C50A could not be expressed normally; in pET32a(+)/BL21 (DE3) trxB- expression system, wild type LTP110 and all mutant proteins could be expressed very well and the levels were higher than that in pTrxFus/GI724 system. LTP110 fusion protein expressed in pET32a(+) vector was purified and its activity was checked by fluorescence labeled fatty acid. Results indicated that the recombinant LTP110 fusion protein has lipid binding activity. This work provides good basis for the further study.

[Expression, purification and function of rice nonspecific lipid transfer protein].

Plant nonspecific lipid transfer protein(nsLTP) is a class of protein which has in vitro lipid transferring activity between biomembranes. In order to study the antimicrobial function of rice nonspecific lipid transfer protein, a gene LTP110 encoding rice nsLTP was cloned into ThioFusion expression vector pET32a (+) and expressed in host strain Bl21(DE3)trxB-. After induction by IPTG at 30 degrees C for 5 h, the fusion protein thio-LTP110 was in large amount produced. The expressed protein was purified by Ni2(+)-chelating Sepharose fast flow column, then digested by enterokinase. By passing through nickel affinity column again, the cleavage product, LTP110, was obtained. CD spectrum scanning from 185 nm to 250 nm showed that the recombinant protein LTP110 had similar secondary structure with the nsLTP purified from rice etiolated seedlings. Activity determination by fluorescent lipid P-96 showed that it had lipid binding activity. Microbial inhibition test results revealed that LTP110 deterred germination of the spores of rice pathogen P. oryzae, showing it might be involved in plant microbial resistance function. Therefore, it has the potential to be used in plant transgene engineering to improve plant resistance.

Purification and Characterization of an Alkaline Lipase from Penicillium cyclopium PG37.

An extracellular, novel alkaline lipase produced by Penicillium cyclopium PG37 was purified by centrifugation, ammonium sulfate precipitation, and phenyl-Sepharose CL-4B, DEAE Sepharose fast flow and Sephadex G-75 column chromatographies. A 16.5-fold purification of the enzyme was achieved which had a specific activity of 5 200 u/mg protein, and the recovery of the activity was 33.2%. The purified enzyme exhibited a single band on SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and polyacrylamide gel electrophoresis (PAGE). The molecular weight of the native lipase was estimated to be about 29 kD by gel filtration using Sephadex G-150, and that of the denatured lipase was determined to be about 27.5 kD by its mobility on SDS-PAGE, indicating that the lipase was a monomer. The N-terminal amino acid sequence was determined with automatic protein sequencer to be ATADAAAFPD, which has no homology with other sequences of known lipases. The optimum temperature of the action of this enzyme was 25 degrees and the lipase was stable below 30 degrees, but only 30% of its activity remained after 20 min incubation at 40 degrees. The enzyme was stable at pH from 6.5 to 10.5, and its optimal pH for activity is 10.0. Low concentration of alkaline proteinase has little effect on the lipase PG37, therefore these two enzymes can be used as ingredients that are added to commercial detergents simultaneously.