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Disparate fluorescence properties of 2-[4'-(iodoacetamido)anilino]-naphthalene-6-sulfonic acid attached to Cys-84 and Cys-35 of troponin C in cardiac muscle troponin.

Abstract：

:Two monocysteine mutants of cardiac muscle troponin C, cTnC(C35S) and cTnC(C84S), were genetically generated and labeled with the fluorescent probe 2-[4'-(iodoacetamido)anilino]naphthalene-6-sulfonic acid (IAANS) at Cys-84 and Cys-35, respectively. Cys-84 is located on helix D in the regulatory N-domain, and Cys-35 is at the -y position of the inactive 12-residue loop of site I. These labeled mutants were studied by a variety of steady-state and time-resolved fluorescence methods. In the absence of divalent cation, the fluorescence of the attached IAANS indicated an exposed environment at Cys-35 and a relatively less-exposed environment at Cys-84. The binding of Ca2+ to the single regulatory site elicited a large enhancement of the emission of IAANS attached to Cys-84, but only marginal fluorescence changes of the probe at Cys-35. Upon reconstitution of the labeled cTnC mutants with troponin I and troponin T to form the three-subunit troponin, the fluorescence of IAANS-Cys-84 in apo-troponin was spectrally similar to that observed with the Ca(2+)-loaded uncomplexed cTnC mutant. Only very moderate changes in the fluorescence of IAANS-Cys-84 were observed when the regulatory site in reconstituted troponin was saturated. The exposed Cys-35 environment of the uncomplexed cTnC mutant became considerably less exposed and less polar when the mutant was incorporated into apo-troponin. In contrast to the Cys-84 site, saturation of the regulatory site II by Ca2+ in reconstituted troponin resulted in a reversal of the environment of the Cys-35 site toward a more exposed and more polar environment. These results indicated involvement of the inactive loop I in the Ca2+ trigger mechanism in cardiac muscle. The fluorescence of IAANS at both Cys-84 and Cys-35 was sensitive to phosphorylation of cTnl in reconstituted troponin, and the sensitivity was observed with both apo-troponin and Ca(2+)-loaded troponin.

journal_name

Biophys J

journal_title

Biophysical journal

authors

Dong WJ,Wang CK,Gordon AM,Cheung HC

doi

10.1016/s0006-3495(97)78719-8

subject

Has Abstract

pub_date

1997-02-01 00:00:00

pages

850-7

issue

2 Pt 1

eissn

0006-3495

issn

1542-0086

pii

S0006-3495(97)78719-8

journal_volume

pub_type

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Disparate fluorescence properties of 2-[4'-(iodoacetamido)anilino]-naphthalene-6-sulfonic acid attached to Cys-84 and Cys-35 of troponin C in cardiac muscle troponin.