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Yogesh Kumar

Publications and source records attributed to Yogesh Kumar.

8 recordsLinked to original sources
PubMed2005

MaxiK channel partners: physiological impact.

The basic functional unit of the large-conductance, voltage- and Ca2+-activated K+ (MaxiK, BK, BKCa) channel is a tetramer of the pore-forming alpha-subunit (MaxiKalpha) encoded by a single gene, Slo, holding multiple alternative exons. Depending on the tissue, MaxiKalpha can associate with modulatory beta-subunits (beta1-beta4) increasing its functional diversity. As MaxiK senses and regulates membrane voltage and intracellular Ca2+, it links cell excitability with cell signalling and metabolism. Thus, MaxiK is a key regulator of vital body functions, like blood flow, uresis, immunity and neurotransmission. Epilepsy with paroxysmal dyskinesia syndrome has been recognized as a MaxiKalpha-related disorder caused by a gain-of-function C-terminus mutation. This channel region is also emerging as a key recognition module containing sequences for MaxiKalpha interaction with its surrounding signalling partners, and its targeting to cell-specific microdomains. The growing list of interacting proteins highlights the possibility that associations with the C-terminus of MaxiKalpha are dynamic and depending on each cellular environment. We speculate that the molecular multiplicity of the C-terminus (and intracellular loops) dictated by alternative exons may modulate or create additional interacting sites in a tissue-specific manner. A challenge is the dissection of MaxiK macromolecular signalling complexes in different tissues and their temporal association/dissociation according to the stimulus.

Animals↗
PubMed2005

Influence of fluoro, chloro and alkyl alcohols on the folding pathway of human serum albumin.

Urea-induced equilibrium unfolding of human serum albumin (HSA) when studied by mean residue ellipticity at 222 nm (MRE(222)) or intrinsic fluorescence measurements showed a two-step, three-state transition with a stable intermediate around 4.6-5.2 M urea. The presence of 2,2,2-trifluoroethanol (TFE) resulted in a single-step, two-state transition with a significant shift towards higher urea concentration, suggesting the stabilizing effect of TFE. The free energy of stabilization (DeltaDeltaG(D)(H(2)O)) in the presence of 3.0 M TFE was determined to be 2.68 and 2.72 kcal/mol by MRE(222) and fluorescence measurements, respectively. The stabilizing potential of other alcohols on the refolding behavior of HSA at 5.0 M urea (where the intermediate exists) as studied by MRE(222) and intrinsic fluorescence measurements showed the following order: 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) > TFE > 2-chloroethanol > tert-butanol > iso-propanol > ethanol > methanol. Further, the extent of refolding at the highest concentration of alcohol was similar in all cases. The stabilizing effect of TFE on guanidine hydrochloride (GdnHCl)-induced unfolding of HSA was nearly equal to that found for urea denaturation, as reflected in the DeltaDeltaG(D)(H(2)O) value (2.38 kcal/mol). Taken together, these results suggest that the stabilizing effect of TFE and other alcohols on urea/GdnHCl-induced unfolding of HSA is higher for alcohols that contain bulky groups or fluorine atoms.

Alcohols↗
PubMed2004

Molten-globule like partially folded states of human serum albumin induced by fluoro and alkyl alcohols at low pH.

Human serum albumin (HSA) exists in a molten-globule like state at low pH (pH 2.0). We studied the effects of trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP) on the acid-denatured state of HSA by far-UV circular dichroism (CD), near-UV CD, tryptophan fluorescence, and 1-anilinonaphthalene-8-sulfonic acid (ANS) binding. At pH 2.0, these alcohols induced the formation of alpha-helical structure as evident from the increase in mean residue ellipticity (MRE) value at 222 nm. On addition of different alcohols, HSA exhibited a transition from the acid-denatured state to the alpha-helical state and loss of ANS-binding sites reflected by the decrease in ANS fluorescence at 480 nm. However, the concentration range required to bring about the transition varied greatly among different alcohols. HFIP was found to have highest potential whereas methanol was least effective in inducing the transition. The order of effectiveness of alcohols was shown to be: HFIP > TFE > 2-chloroethanol > tert-butanol > isopropanol > ethanol > methanol as evident from the Cm values. The near-UV CD spectra and tryptophan fluorescence showed the differential effects of halogenated alcohols with those of alkanols. A comparison of the m values, showing the dependence of Delta GH on alcohol concentration, suggests that the helix stabilizing potential of different alcohols is due to the additive effect of different constituent groups present whereas remarkably higher potential of HFIP involves some other factor in addition to the contribution of constituent groups.

Alcohols↗
PubMed2003

Behavior of various mammalian albumins towards bilirubin binding and photochemical properties of different bilirubin-albumin complexes.

Bilirubin (BR) binding properties of serum albumins from different mammalian species viz. human (HSA), equine (ESA), dog (DSA) and guinea pig (GPSA) were studied by absorption, fluorescence and CD spectroscopy. Whereas, a complex of BR with ESA produced maximum change, GPSA-BR complex showed weaker interaction as reflected from absorption and fluorescence spectroscopic data. Conformational analysis of these albumins by near- and far-UV CD spectra suggested similar structural characteristics (both secondary and tertiary structures) for ESA and HSA, whereas, DSA and GPSA had lower amounts of secondary and tertiary structures being minimum for GPSA. Photoirradiation results of BR-albumin complexes showed GPSA-bound BR more labile compared with other complexes, whereas, BR-ESA complex was found to be more stable against photoinduced chemical changes. Taken together, all these results suggest that chiroptical properties/stability of albumin bound BR varies with albumin species.

Albumins↗
PubMed2002

Bilirubin binding properties of pigeon serum albumin and its comparison with human serum albumin.

Binding of bilirubin (BR) to pigeon serum albumin (PgSA) was studied by absorption, fluorescence and CD spectroscopy and results were compared with those obtained with human serum albumin (HSA). PgSA was found to be structurally similar to HSA as judged by near- and far-UV CD spectra. However, PgSA lacks tryptophan. Binding of BR to PgSA showed relatively weaker interaction compared to HSA in terms of binding affinity, induced red shift in the absorption spectrum of BR and CD spectral characteristics of BR-albumin complexes. Photoirradiation results of BR-albumin complexes also showed PgSA-bound BR more labile compared to HSA-bound BR.

Animals↗
PubMed2002

Salt-induced refolding in different domains of partially folded bovine serum albumin.

In our earlier communication on urea denaturation of bovine serum albumin (BSA), we showed significant unfolding of domain III along with domain I prior to intermediate formation around 4.6-5.2 M urea based on the binding results of domain specific ligands:chloroform, bilirubin and diazepam for domains I, II and III, respectively. Here, we present our results on the salt-induced refolding of the two partially folded states of BSA obtained at 4.5 M urea and at pH 3.5, respectively. Both these states were characterized by significant unfolding of both domains I and III as indicated by decreased binding of chloroform and diazepam, respectively. Salt-induced stabilization of partially folded states of BSA was accompanied by nearly complete refolding of both domains I and III as the binding isotherms of chloroform and diazepam obtained in presence of approximately 1.0 M KCl were nearly identical to that obtained with native BSA at pH 7.4. From these observations, it can be concluded that the anion binding sites on serum albumin are not only confined to domain III (C-terminal region) but few sites are also present on domain I (or N-terminal region) of the protein.

Animals↗
PubMedDate not supplied

Standardisation and comparison of serial dilution and single dilution enzyme linked immunosorbent assay (ELISA) using different antigenic preparations of the Babesia (Theileria) equi parasite.

Serial dilution and single dilution enzyme linked immunosorbent assays (ELISA) were standardised and their sensitivity and specificity were compared for serodiagnosis of Babesia equi infection. The antibody titres of 24 donkey sera of known identity were determined separately by serial dilution ELISA using three different B. equi antigens namely whole merozoite (WM), cell membrane (CM) and high speed supernatant (HSS). The ratios of the optical density (OD) of known positive and known negative sera at different serum dilutions were calculated and termed as the positive/negative (P/N) ratio. The coefficients of correlation (r) were calculated between the P/N ratios at different dilutions of sera and the log10 antibody titres of the same sera were ascertained by serial dilution ELISA. The highest value of 'r' was obtained at a serum dilution of 1:200. From log10 antibody titre of sera (y) and their P/N ratio at a dilution of 1:200 (x), regression equations (y = a + bx) were calculated separately for the three antigens. Test sera were diluted to 1:200, their OD were read in duplicate wells and were converted to the P/N ratio. Antibody titres were predicted from the P/N ratio using a regression equation separately for the three antigens. Titres obtained by both ELISAs were not significantly different from each other, thus confirming that single dilution ELISA could be successfully used to replace conventional serial dilution ELISA. The sensitivity, specificity and predictive value of single dilution ELISA was validated statistically using 42 B. equi disease-positive sera and 106 B. equi disease-negative sera. The WM antigen was found to be the most sensitive with a higher predictive value for negative test sera as compared to the CM or HSS antigens. Sera positive for other equine infections including Babesia caballi showed no cross-reaction with the three B. equi antigens in ELISA, thus the test was immunologically specific. Antibody titres of 109 unknown field donkey/horse sera obtained by serial and single dilution ELISA using the WM antigen did not show any significant difference. Since the single dilution ELISA was found to be more economical, convenient, sensitive, specific than the serial dilution ELISA and has a high predictive value, it is suitable for use in sero-epidemiological studies on B. equi infections in the field.

Animals↗