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J T Welch

Publications and source records attributed to J T Welch.

At least 19 recordsLinked to original sources
PubMed2001

Chimeric HTH motifs based on EF-hands.

The design of a new peptide construct from two structurally equivalent basis motifs is reported. A chimera was designed from the helical regions of a helix-turn-helix (HTH) domain, incorporating the consensus EF-hand Ca-binding loop at the turn. Two 33-residue peptides were constructed: one (P3, designed) includes the 12-residue consensus EF-hand loop, while the other (P2, control) contains the reversed EF-hand loop sequence. The Eu(III) and Ca(II) binding properties of P2 and P3 were investigated by circular dichroism and NMR. The designed peptide (P3) is 25% helical in its Eu(III)-saturated form, and 14% helical with excess Ca(II). Both the free and Eu-bound peptides have inherent solution structure, as demonstrated by the helicity induced by the addition of trifluoroethanol solvent. While Eu(III) binding stabilizes the structure of P3, it destabilizes the structure of P2. The NMR titration of P3 with Eu(III) resulted in new resonances characteristic of Ca-bound EF-hand loops. As observed for isolated EF-hands, the resonances appear within the first 0.5 equivalents of Eu(III) added, suggesting that one metal ion organizes two equivalents of peptide to fold into the back-to-back dimer structure of native EF-hands. The EuP3 chimera, but not EuP2, has significant affinity for supercoiled plasmid DNA, causing a gel shift at concentrations as low as 10 microM EuP3 (50 microM base pairs). These results show our chimeric peptide combines the characteristics of the parent motifs, maintaining both metal binding and DNA affinity.

Amino Acid Motifs↗
PubMed2000

Pyrazinamide inhibits the eukaryotic-like fatty acid synthetase I (FASI) of Mycobacterium tuberculosis.

Tuberculosis treatment is shortened to six months by the indispensable addition of pyrazinamide (PZA) to the drug regimen that includes isoniazid and rifampin. PZA is a pro-drug of pyrazinoic acid (POA) (ref. 3), whose target of action has never been identified. Although PZA is active only against Mycobacterium tuberculosis, the PZA analog 5-chloro-pyrazinamide (5-Cl-PZA) displays a broader range of anti-mycobacterial activity. We have found that the eukaryotic-like fas1 gene (encoding fatty acid synthetase I, FASI) from M. avium, M. bovis BCG or M. tuberculosis confers resistance to 5-Cl-PZA when present on multi-copy vectors in M. smegmatis. 5-Cl-PZA and PZA markedly inhibited the activity of M. tuberculosis FASI, the biosynthesis of C16 to C24/C26 fatty acids from acetyl-CoA (ref. 6). Importantly, PZA inhibited FASI in M. tuberculosis in correlation with PZA susceptibility. These results indicate that FASI is a primary target of action for PZA in M. tuberculosis. Further characterization of FASI as a drug target for PZA may allow the development of new drugs to shorten the therapy against M. tuberculosis and may provide more options for treatment against M. bovis, M. avium and drug resistant M. tuberculosis.

Animals↗
PubMed1998

Inhibition of dipeptidyl peptidase IV by fluoroolefin-containing N-peptidyl-O-hydroxylamine peptidomimetics.

Dipeptidyl peptidase IV (EC 3.4.14.5; DPP IV), also known as the leukocyte differentiation antigen CD26 when found as an extracellular membrane-bound proline specific serine protease, cleaves a dipeptide from the N terminus of a polypeptide chain containing a proline residue in the penultimate position. Here we report that known (Z)-Ala-psi[CF=C]-Pro dipeptide isosteres 1 and 2, which contain O-acylhydroxylamines, were isolated as diastereomeric pairs u-1, l-1, and l-2. The effect of each diastereomeric pair as an inhibitor of human placental dipeptidyl peptidase DPP IV has been examined. The inhibition of DPP IV by these compounds is rapid and efficient. The diastereomeric pair u-1 exhibits very potent inhibitory activity with a Ki of 188 nM. Fluoroolefin containing N-peptidyl-O-hydroxylamine peptidomimetics, by virtue of their inhibitory potency and stability, are superior to N-peptidyl-O-hydroxylamine inhibitors derived from an Ala-Pro dipeptide.

Crystallography, X-Ray↗
PubMed1998

In vitro antimycobacterial activity of 5-chloropyrazinamide.

5-Chloropyrazinamide and 5-chloropyrazinoic acid were evaluated for in vitro activity against Mycobacterium tuberculosis, Mycobacterium bovis, and several nontuberculous mycobacteria by a broth dilution method. 5-Chloropyrazinamide was more active than pyrazinamide against all organisms tested. It is likely that this agent has a different mechanism of action than pyrazinamide.

Antitubercular Agents↗
PubMed1996

Quantitative structure-activity relationships for the in vitro antimycobacterial activity of pyrazinoic acid esters.

Substituted pyrazinoic acid esters have previously been reported to have in vitro activity against Mycobacterium avium and Mycobacterium kansasii as well as Mycobacterium tuberculosis. Modification of both the pyrazine nucleus and the ester functionality was successful in expanding the antimycobacterial activity associated with pyrazinamide to include M. avium and M. kansasii, organisms usually not susceptible to pyrazinamide. In an attempt to understand the relationship between the activity of the esters with the needed biostability, a quantitative structure-activity relationship has been developed. This derived relationship is consistent with the observation that tert-butyl 5-chloropyrazinoate (13) and 2'-(2'-methyldecyl) 5-chloropyrazinoate (25), compounds which are both 100-fold more active than pyrazinamide against M. tuberculosis and possess a serum stability 900-1000 times greater than the lead compounds in the series.

AIDS-Related Opportunistic Infections↗
PubMed1995

Pyrazinoic acid esters with broad spectrum in vitro antimycobacterial activity.

A series of substituted pyrazinoic acid esters has been prepared and examined for their in vitro activity against Mycobacterium avium and Mycobacterium kansasii as well as Mycobacterium tuberculosis. Modification of both the pyrazine nucleus and the ester functionality have been very successful in expanding the activity of pyrazinamide to include M. avium and M. kansasii, organisms normally not susceptible to pyrazinamide. Several of these compounds have activities 100-1000-fold greater than that of pyrazinamide against M. tuberculosis.

Anti-Bacterial Agents↗
PubMed1995

Activity of n-propyl pyrazinoate against pyrazinamide-resistant Mycobacterium tuberculosis: investigations into mechanism of action of and mechanism of resistance to pyrazinamide.

The mechanism of action of pyrazinamide (PZA) is not known. One hypothesis is that PZA functions as a prodrug of pyrazinoic acid. Susceptibility to PZA correlates with amidase activity of the Mycobacterium tuberculosis isolate in question. PZA-resistant isolates retain susceptibility in vitro to pyrazinoic acid and n-propyl pyrazinoate. Esters of pyrazinoic acid appear to circumvent the requirement for activation by mycobacterial amidase. The MICs of n-propyl pyrazinoate for M. tuberculosis isolates are lower than those of pyrazinoic acid. Further studies to assess the effects of modifications of the alcohol and pyrazine moieties of pyrazinoate esters on in vitro and in vivo antituberculosis activity are under way. This may lead to a candidate compound with enhanced activity against both PZA-susceptible and PZA-resistant M. tuberculosis isolates suitable for clinical development.

Amidohydrolases↗
PubMed1993

The synthesis of 2,3-dideoxy-2-fluoro-3-C-methylpentose-containing nucleosides via [3,3]-sigmatropic rearrangements.

[3,3]-Sigmatropic rearrangement of in situ-formed [O,O]-silyl ketene acetals of butenyl fluoroacetates was used as the key step in the synthesis of racemic 2,3-dideoxy-2-fluoro-3-C-methylpentofuranoses. The product pentofuranoses were transformed further into pyrimidine and purine nucleosides. The conformations of the synthetic carbohydrates were confirmed by single-crystal X-ray diffraction studies and indicated that previous structural assignments made by NMR were in error.

Crystallography, X-Ray↗
PubMed1992

Antimycobacterial activity of a series of pyrazinoic acid esters.

A series of pyrazinoic acid esters has been prepared and evaluated for in vitro antimycobacterial activity. Several of the pyrazinoate esters have substantially better activity than the first-line antituberculous agent pyrazinamide against susceptible isolates of Mycobacterium turberculosis as well as activity against pyrazinamide-resistant isolates. The minimal inhibitory concentrations (MICs) were lower for each organism and at each pH than the MICs for pyrazinamide. The esters have activity against Mycobacterium bovis and Mycobacterium kansasii, two species resistant to pyrazinamide, but not against Mycobacterium avium complex.

Animals↗