Calmodulin-RS20-Ca

₄ complex in the gas phase: electrospray ionisation and Fourier transform ion cyclotron resonance

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Eur. J. Mass Spectrom. 7, 393 - 398 (2001)

Calmodulin-RS20-Ca₄ complex in the gas phase: electrospray ionisation and Fourier transform ion cyclotron resonance

Marjaana Nousiainen and Pirjo Vainiotalo
Department of Chemistry, University of Joensuu, PO Box 111, FIN-80101 Joensuu, Finland
Xidong Feng and Peter J. Derrick^*
Institute of Mass Spectrometry and Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK E-mail:

ABSTRACT:

Dissociation of the complex between calmodulin, four calcium ions and the synthetic peptide RS20 derived from the phosphorylation site of smooth-muscle myosin light-chain kinase was studied by sustained off-resonance irradiation/collision-induced dissociation (SORI-CID) and electrospray ionisation (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Gas-phase dissociation of isolated ions of calmodulin-RS20-Ca₄ in the 8+ charge state yielded fragments via two parallel pathways; calmodulin-Ca₄ complex ions in 5+ and 6+ charge states and RS20 ions in 2+ and 3+ charge states were detected at high resolution. The results are interpreted as indicating that RS20 binding to calmodulin in this complex is specific, involving particular non-covalent interactions that decompose readily during collision-induced dissociation. More specifically, it is proposed that the gas-phase dissociation of calmodulin-RS20-Ca₄ complex reflects the existence in vacuo of salt bridges.

Keywords: calmodulin, electrospray ionisation, Fourier transform ion cyclotron resonance (FT-ICR), non-covalent interaction, dissociation

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