Isolation and characterization of isoforms of HspBP1, inhibitors of Hsp70

Molecular genetic analysis of midgut serine proteases in Aedes aegypti mosquitoes

Digestion of blood meal proteins by midgut proteases provides anautogenous mosquitoes with the nutrients required to complete the gonotrophic cycle. Inhibition of protein digestion in the midgut of blood feeding mosquitoes could therefore provide a strategy for population control. Based on recent reports indicating that the mechanism and regulation of protein digestion in blood fed female Aedes aegypti mosquitoes is more complex than previously thought, we used a robust RNAi knockdown method to investigate the role of four highly expressed midgut serine proteases in blood meal metabolism. We show by Western blotting that the early phase trypsin protein (AaET) is maximally expressed at 3 h post-blood meal (PBM), and that AaET is not required for the protein expression of three late phase serine proteases, AaLT (late trypsin), AaSPVI (5G1), and AaSPVII. Using the trypsin substrate analog BApNA to analyze in vitro enzyme activity in midgut extracts from single mosquitoes, we found that knockdown of AaSPVI expression caused a 77.6% decrease in late phase trypsin-like activity, whereas, knockdown of AaLT and AaSPVII expression had no significant effect on BApNA activity. In contrast, injection of AaLT, AaSPVI, and AaSPVII dsRNA inhibited degradation of endogenous serum albumin protein using an in vivo protease assay, as well as, significantly decreased egg production in both the first and second gonotrophic cycles (P < 0.001). These results demonstrate that AaLT, AaSPVI, and AaSPVII all contribute to blood protein digestion and oocyte maturation, even though AaSPVI is the only abundant midgut late phase serine protease that appears to function as a classic trypsin enzyme.

Dissection of the ATP-binding domain of the chaperone hsc70 for interaction with the cofactor Hap46

Several unrelated proteins are known that specifically interact with members of the mammalian hsp70 chaperone protein family independent of the hsp70 substrate-binding site. One of these is Hap46, also called BAG-1, which binds to the ATP-binding domain of hsp70 and its constitutively expressed, highly homologous counterpart hsc70, thereby affecting nucleotide binding, as well as protein folding properties, of these molecular chaperones. In an attempt to delineate the potential contact sites on hsp70/hsc70 involved in this interaction we made use of the following two independent approaches: (i) screening of membrane-bound peptide libraries based on the sequence of the ATP-binding domain and (ii) the phage-display technique with random dodecapeptides. These approaches yielded partially overlapping results and identified several possible contact regions. On the space-filling model of hsc70, the two major contact areas for Hap46 delineated in the present study are located on the same side of the molecule on either subdomain that border the central cleft harboring the nucleotide-binding site. We suggest that this bridging affects the conformation of the ATP-binding domain in a way similar to the opening of the nucleotide-binding cleft produced in the bacterial hsp70 homologue DnaK upon binding its regulatory protein GrpE.

LHS1 and SIL1 provide a lumenal function that is essential for protein translocation into the endoplasmic reticulum

Lhs1p is an Hsp70-related chaperone localized in the endoplasmic reticulum (ER) lumen. Deltalhs1 mutant cells are viable but are constitutively induced for the unfolded protein response (UPR). Here, we demonstrate a severe growth defect in Deltaire1Deltalhs1 double mutant cells in which the UPR can no longer be induced. In addition, we have identified a UPR- regulated gene, SIL1, whose overexpression is sufficient to suppress the Deltaire1Deltalhs1 growth defect. SIL1 encodes an ER-localized protein that interacts directly with the ATPase domain of Kar2p (BiP), suggesting some role in modulating the activity of this vital chaperone. SIL1 is a non-essential gene but the Deltalhs1Deltasil1 double mutation is lethal and correlates with a complete block of protein translocation into the ER. We conclude that the IRE1-dependent induction of SIL1 is a vital adaptation in Deltalhs1 cells, and that the activities associated with the Lhs1 and Sil1 proteins constitute an essential function required for protein translocation into the ER. The Sil1 protein appears widespread amongst eukaryotes, with homologues in Yarrowia lipolytica (Sls1p), Drosophila and mammals.