Much attention is focused on the benzoquinone ansamycins as anticancer agents, with several derivatives of the natural product geldanamycin (GdA) now in clinical trials. These drugs are selective inhibitors of Hsp90, a molecular chaperone vital for many of the activities that drive cancer progression. Mutational changes to their interaction site, the extremely conserved ATP binding site of Hsp90, would mostly be predicted to inactivate the chaperone. As a result, drug resistance should not arise readily this way. Nevertheless, Streptomyces hygroscopicus, the actinomycete that produces GdA, has evolved an Hsp90 family protein (HtpG) that lacks GdA binding. It is altered in certain of the highly conserved amino acids making contacts to this antibiotic in crystal structures of GdA bound to eukaryotic forms of Hsp90. Two of these amino acid changes, located on one side of the nucleotide-binding cleft, weakened GdA/Hsp90 binding and conferred partial GdA resistance when inserted into the endogenous Hsp90 of yeast cells. Crystal structures revealed their main effect to be a weakening of interactions with the C-12 methoxy group of the GdA ansamycin ring. This is the first study to demonstrate that partial GdA resistance is possible by mutation within the ATP binding pocket of Hsp90.

It is approximately 60 years since the discovery of cephalosporin C in Cephalosporium acremonium. Streptomycetes have since been found to produce the structurally related cephamycin C. Studies on the biosynthetic pathways of these two compounds revealed a common pathway including a step governed by deacetoxycephalosporin C synthase which catalyses the ring-expansion of penicillin N to deacetoxycephalosporin C. Because of the therapeutic importance of cephalosporins, this enzyme has been extensively studied for its ability to produce these antibiotics. Although, on the basis of earlier studies, its substrate specificity was believed to be extremely narrow, relentless efforts in optimizing the in-vitro enzyme assay conditions showed that it is able to convert a wide range of penicillin substrates differing in their side chains. It is a member of 2-oxoglutarate-dependent dioxygenase protein family, which requires the iron(II) ion as a co-factor and 2-oxoglutarate and molecular oxygen as co-substrates. It has highly conserved HXDX( n ) H and RXS motifs to bind the co-factor and co-substrate, respectively. With advances in technology, the genes encoding this enzyme from various sources have been cloned and heterologously expressed for comparative analyses and mutagenesis studies. A high level of recombinant protein expression has also enabled crystallization of this enzyme for structure determination. This review will summarize some of the earlier biochemical characterization and describe the mechanistic action of this enzyme revealed by recent structural studies. This review will also discuss some of the approaches used to identify the amino acid residues involved in binding the penicillin substrate and to modify its substrate preference for possible industrial application.

Co-chaperones are well-known regulators of heat shock protein 90 (Hsp90). Hsp90 is a molecular chaperone that is essential in the eukaryotes for the folding and activation of numerous proteins involved in important cellular processes such as signal transduction, growth and developmental regulation. Co-chaperones assist Hsp90 in the protein folding process by modulating conformational changes to promote client protein interaction and functional maturation. With the recognition of Plasmodium falciparum Hsp90 (PfHsp90) as a potential antimalarial drug target, there is obvious interest in the study of its co-chaperones in their partnership in regulating cellular processes in malaria parasite. Previous studies on PfHsp90 have identified more than 10 co-chaperones in P. falciparum genome. However, many of them remained annotated as putative proteins as their functionality has not been validated experimentally. So far, only five co-chaperones, PfHop, Pfp23, PfAha1, PfPP5 and PfFKBP35 have been characterized and shown to interact with PfHsp90. This review will summarize current knowledge on the co-chaperones in P. falciparum and discuss their regulatory roles on PfHsp90. As certain eukaryotic co-chaperones have also been implicated in altering the affinity of Hsp90 for its inhibitor, this review will also examine plasmodial co-chaperones' potential influence on approaches towards designing antimalarials targeting PfHsp90.

It is well known that the co-chaperone p23 regulates Hsp90 chaperone activity in protein folding. In Plasmodium falciparum, a putative p23 (Pfp23) has been identified through genome analysis, but its authenticity has remained unconfirmed since co-immunoprecipitation experiments failed to show its interaction with P. falciparum Hsp90 (PfHsp90). Thus, recombinant Pfp23 and PfHsp90 proteins purified from expressed clones were used in this study. It was clear that Pfp23 exhibited chaperone activity by virtue of its ability to suppress citrate synthase aggregation at 45 degrees C. Pfp23 was also shown to interact with PfHsp90 and to suppress its ATPase activity. Analyses of modeled Pfp23-PfHsp90 protein complex and site-directed mutagenesis further revealed strategically placed amino acid residues, K91, H93, W94 and K96, in Pfp23 to be crucial for binding PfHsp90. Collectively, this study has provided experimental evidence for the inherent chaperone function of Pfp23 and its interaction with PfHsp90, a sequel widely required for client protein activation.

Microbial loads in freshwater systems have important implications in biogeochemical cycling in urban environments. Immersed surfaces in freshwaters provide surfaces for bacterial attachment and growth. Microorganisms that adhere initially to these surfaces play a critical role in biofilm formation and sustenance. Currently, there is little understanding on the type of organisms that initially adhere to different surfaces in urban canals. In this study, water from an urban stormwater canal was employed to allow bacteria to attach to different surfaces in a flowcell apparatus and understand the differences and changes in bacterial community structure. Bacterial communities were highly diverse on different surfaces as indicated by Jaccard's indices of 0.14-0.56. Bacteria on aluminium were the most diverse and on Plexiglas the least. Bacterial communities were highly dynamic in the early attachment phase and it changed by 59% between 3 and 6 h on aluminium. Specificity of attachment to surfaces was observed for some bacteria. Judicious use of materials in urban aquatic environment would help mitigate microbial load in urban waters.