To study the role of the hinge region in nisin and to obtain mutants that exhibit altered or new biological activities and functional properties, we changed certain amino acids in the hinge region by performing site-directed mutagenesis with the nisinZ structural gene ( nisZ). The results showed that the nisinZ mutants had decreased antimicrobial activities against Micrococcus flavus NCIB8166 and Streptococcus thermophilus. Interestingly, compared with wild nisinZ, mutant N20K nisinZ and M21K nisinZ displayed antimicrobial activity against gram-negative Shigella, Pseudomonas and Salmonella; and they had a higher solubility than wild-type nisinZ. At pH 8, the solubilities of N20K nisinZ and M21K nisinZ were, respectively, three-fold higher and five-fold higher than that of nisinZ. Mutant N20Q nisinZ and M21G nisinZ were considerably more stable than nisinZ at higher temperatures and neutral or alkaline pH. These mutants provided information that the central hinge region in nisinZ plays an important role in providing the conformational flexibility required for the antimicrobial activity on the membrane. Our finding documented that it may well be worth considering the construction of the new nisin mutants with changed inhibitory activity against a wide range of gram-negative bacteria and the improvement of functional properties by site-directed mutagenesis.

Hybrid glass/polytetrafluoroethylene (PTFE) fabric composites filled with micrometre Synfluo 180XF wax (SFW) and nano-SiO 2 were prepared by dip coating of hybrid glass/PTFE fabric in phenolic adhesive resin containing the particles to be incorporated and successive curing. The friction and wear behaviours of these hybrid composites sliding against AISI-1045 steel in a pin on disc configuration were evaluated on a high temperature friction and wear tester. The composite structures and the morphologies of the worn surfaces were analysed by means of scanning electron microscopy. The results show that the addition of SFW and nano-SiO 2 can improve the wear resistance and friction reduction in the hybrid composite, and the addition of nano-SiO 2 endows the composite with best triboperformance. The improved triboperformance of nano-SiO 2 or SFW filled hybrid glass/PTFE fabric composites can be attributed to the self-lubricating properties of filler, the improved structural stability and the special characteristics of transfer film.