Soaking in Cs₂SO₄ reveals a caesium‐aromatic interaction in bovine‐liver rhodanese

Abstract

Soaking crystals of rhodanese (thiosulphate : cyanide sulphurtransferase) in 2 M caesium sulphate reveals three caesium binding sites of this enzyme. One of these had been described before as a binding site for sodium ions and is located in a cleft close to the active site. In this site the monovalent cation is coordinated by five oxygen atoms. The first additional binding site seems to be quite special. The caesium ion is bound to the phenyl ring of a tryptophan residue. It is further liganded by two oxygen atoms. The third binding site is a result of crystal packing effects: caesium is liganded by four oxygen atoms, provided by two rhodanese molecules and one sulphate ion.It is likely that the binding of caesium affects the fluorescence of the tryptophan residue with which it interacts. Such possible effects should also be kept in mind when caesium ions are used as a quencher in fluorescence studies of proteins in general.

Functional Complementation of the Essential Gene fabG1 of Mycobacterium tuberculosis by Mycobacterium smegmatis fabG but Not Escherichia coli fabG

“…5D). The pseudomolecular mass (MϩNa) ϩ peaks observed in the spectra corresponded to the peaks determined previously for the mycolates synthesized by the wild-type strain of M. tuberculosis (strain H37Rv) (10). No additional lipid spots or structural changes in the transformants were detected by TLC and MALDI-TOF mass spectrometry (data not shown).…”

Tracking the Putative Biosynthetic Precursors of Oxygenated Mycolates of Mycobacterium tuberculosis

“…Revelation of lipid spots was performed by spraying the plates with molybdophosphoric acid (10% in ethanol), followed by charring. The crude mycolate fraction was obtained by precipitating an ethereal solution of fatty acid methyl esters with methanol at 4°C, followed by centrifugation at 4000 ϫ g for 20 min (24). The different classes of mycolates were separated by chromatography on a Florisil column irrigated with increasing concentrations of diethyl ether (0, 10, 20, 30, and 50%, v/v) in petroleum ether, and purification was achieved by preparative TLC using eluent A (17).…”

“…Nevertheless, it is currently admitted that the two known mycobacterial fatty-acid synthases (FAS) 1 participate in the formation of all types of mycolates or their precursors. FAS-I, a synthase that has been shown to be a bimodal system, is necessary to produce C 16,18 and C [22][23][24][25][26] saturated fatty acids, which may be either directly incorporated in mycolates as the ␣-branch chain or used as substrates of the elongation system, FAS-II. The finding that isoniazid strongly and specifically inhibits InhA, an enoyl-acyl carrier protein reductase that belongs to FAS-II (13)(14), is consistent with the proposed biosynthetic pathway leading to the various types of mycolates.…”

Structure of a Hydroxymycolic Acid Potentially Involved in the Synthesis of Oxygenated Mycolic Acids of the Mycobacterium Tuberculosis Complex

“…The different types of mycolic acid were identified by comparison with authentic standards [23]. For purification, fatty acids were extracted as described above; mycolic acids were precipitated with methanol as previously described [24] and methylated. For mass spectrometry analysis, each type of mycolate was directly purified by preparative TLC after two elutions in dichloromethane.…”