The length of glycine-rich linker in DNA-binding domain is critical for optimal functioning of quorum-sensing master regulatory protein HapR.

HapR is a quorum-sensing master regulatory protein in Vibrio cholerae. Though many facts are known regarding its structural and functional aspects, much still can be learnt from natural variants of this wild-type protein. While unraveling the underlying cause of functional inertness of a natural variant (HapRV2), the significance of a conserved glycine residue at position 39 in a glycine-rich linker in DNA-binding domain comes into light. This work aims at investigating how the length of glycine-rich linker (R(33)GIGRGG(39)) bridging helices α1 and α2 modulates the functionality of HapR. In pursuit of our interest, glycine residues were inserted after terminal glycine (G39) of the linker in a sequential manner. To evaluate functionality, all the glycine linker variants were subjected to a battery of performance tests under various conditions. Combined in vitro and in vivo results clearly demonstrated a gradual functional impairment of HapR linker variants coupled with increasing length of glycine-rich linker and finally, linker variant harboring four glycine residues resulted in a functionally compromised protein with significant loss of communication with cognate DNAs. Molecular dynamics studies of modeled HapR linker variants in complex with cognate promoter region show that residues namely Ser50, Thr53 and Asn56 are involved in varying degree of interactions with different nucleotides of HapR-DNA complex. The diminished functionality between variants and DNA appears to result from reduced or no interactions between Phe55 and nucleotides of cognate DNA as observed during simulations.

Evidence on how a conserved glycine in the hinge region of HapR regulates its DNA binding ability: lessons from a natural variant.

HapR has been recognized as a quorum-sensing master regulator in Vibrio cholerae. Because it controls a plethora of disparate cellular events, the absence of a functional HapR affects the physiology of V. cholerae to a great extent. In the current study, we pursued an understanding of an observation of a natural protease-deficient non-O1, non-O139 variant V. cholerae strain V2. Intriguingly, a nonfunctional HapR (henceforth designated as HapR(V2)) harboring a substitution of glycine to aspartate at position 39 of the N-terminal hinge region has been identified. An in vitro gel shift assay clearly suggested the inability of HapR(V2) to interact with various cognate promoters. Reinstatement of glycine at position 39 restores DNA binding ability of HapR(V2) (HapR(V2G)), thereby rescuing the protease-negative phenotype of this strain. The elution profile of HapR(V2) and HapR(V2G) proteins in size-exclusion chromatography and their circular dichroism spectra did not reflect any significant differences to explain the functional discrepancies between the two proteins. To gain insight into the structure-function relationship of these two proteins, we acquired small/wide angle x-ray scattering data from samples of the native and G39D mutant. Although Guinier analysis and indirect Fourier transformation of scattering indicated only a slight difference in the shape parameters, structure reconstruction using dummy amino acids concluded that although HapR adopts a "Y" shape similar to its crystal structure, the G39D mutation in hinge drastically altered the DNA binding domains by bringing them in close proximity. This altered spatial orientation of the helix-turn-helix domains in this natural variant provides the first structural evidence on the functional role of the hinge region in quorum sensing-related DNA-binding regulatory proteins of Vibrio spp.

Substitution of glutamate residue by lysine in the dimerization domain affects DNA binding ability of HapR by inducing structural deformity in the DNA binding domain.

HapR has been given the status of a high cell density master regulatory protein in Vibrio cholerae. Though many facts are known regarding its structural and functional aspects, much still can be learnt from natural variants of the wild type protein. This work aims at investigating the nature of functional inertness of a HapR natural variant harboring a substitution of a conserved glutamate residue at position 117 which participates in forming a salt bridge by lysine (HapRV2G-E(117)K). Experimental evidence presented here reveals the inability of this variant to interact with various cognate promoters by in vitro gel shift assay. Furthermore, the elution profiles of HapRV2G-E(117)K protein along with the wild type functional HapRV2G in size-exclusion chromatography as well as circular dichroism spectra did not reflect any significant differences in its structure, thereby indicating the intactness of dimer in the variant protein. To gain further insight into the global shape of the proteins, small angle X-ray scattering analysis (SAXS) was performed. Intriguingly, increased radius of gyration of HapRV2G-E(117)K of 27.5 Å in comparison to the wild type protein from SAXS data analyses implied a significant alteration in the global shape of the dimeric HapRV2G-E(117)K protein. Structure reconstruction brought forth that the DNA binding domains were substantially "parted away" in this variant. Taken together, our data illustrates that substitution of the conserved glutamate residue by lysine in the dimerization domain induces separation of the two DNA binding domains from their native-like positioning without altering the dimeric status of HapR variant.

VopF, a type III effector protein from a non-O1, non-O139 Vibrio cholerae strain, demonstrates toxicity in a Saccharomyces cerevisiae model.

VopF, a type III effector protein, has been identified as a contributory factor to the intestinal colonization of type III secretion system-positive, non-O1, non-O139 Vibrio cholerae strains. To gain more insight into the function of VopF, a yeast model was developed. Using this model, it was found that ectopic expression of VopF conferred toxicity in yeast.

Quality of life as a key indicator of patient satisfaction and treatment compliance in people with type 2 diabetes mellitus in the IMPROVE study: a multicentre, open label, non-randomised, observational trial.

Diabetes is a debilitating chronic illness having multiple impacts on physical and mental well-being of patients. When treating chronic conditions like diabetes, psychosocial aspects and quality of life (QoL) have to be considered; however, these receive less attention due to various reasons. Patients with diabetic complications have increased levels of depression and decreased QoL This necessitates evaluating QoL of patient which now is used as a primary or secondary end point in clinical trials eg, Diab-MedSat QoL questionnaire used in diabetes. At some point all diabetic patients may require insulin to control hyperglycaemia and disease progression. The traditional insulin syringe and needle delivery system has been the principal barrier in the treatment of diabetes as it was not well accepted among the patients due to various reasons. A success over this approach has been pen like devices like FlexPen and Novopen3 which are becoming more popular than the conventional syringe-and-needles as they have several advantages like, easy to carry, use, maintain and also reduces administrative errors ensuring accurate doses are delivered. The objective of IMPROVE study is to evaluate the safety and effectiveness of biphasic insulin aspart (NovoMix 30) in normal clinical practice conditions, in India. This is an open label, non-randomised, non-interventional, observational, safety and effectiveness study in approximately 17,995 patients with type 2 diabetes mellitus. A cohort of Indian patients (n = 349) from all 4 geographical locations (North, West, East and South of India) were administered QoL instrument Diab-MedSat at baseline and 346 patients at final visit (n = 346) to assess their satisfaction with the treatment they received. The results were included in the final statistical analysis as additional outcome variables. The Diab-MedSat Novo Nordisk June 2004 English (UK) version is used. The Diab-MedSat has 21 items that need to be answered and it is scored as an overall score (all 21 items) as well as three subscale scores regarding burden (11 items), symptoms (5 items), efficacy (5 items). The complete analysis took into account all 21 items of Diab-MedSat questionnaire with their subscales. Analyses of the cohort showed higher patient satisfaction among the patients administered Diab-MedSat questionnaire from baseline (n = 349) to final visit (n = 346). The mean of overall score was 52.33 (baseline visit) versus 79.03 (final visit). The difference in the overall score and sub parameters like burden, symptoms and efficacy between the baseline and final visits were statistically significant (p-value < 0.001). The mean value of difference in overall score between the baseline visit and final visit was 26.73 +/- 20.83; while the difference for burden, symptoms and efficacy were respectively 27.86 +/- 20.81, 19.75 +/- 20.94 and 32.87 +/- 28.08. A fairly clear picture emerged that the use of biphasic insulin aspart resulted in improved QoL of the patients substantially. This is demonstrated in the results for all the parameters that were used like symptoms, efficacy and burden. The overall number of extremely satisfied patients had increased from 5.4% in the baseline visit to 91% in the final visit. This unambiguously proves that the satisfaction of patients on biphasic insulin aspart (NovoMix 30) is beyond question.