Circular dichroism and 1H NMR studies of Co2+- and Ni2+-substituted concanavalin A and the lentil and pea lectins.

I. Bertini, M. S. Viezzoli, C. Luchinat, E. Stafford, A. D. Cardin, W. D. Behnke, L. Bhattacharyya, C. F. Brewer

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Abstract

Visible absorption, circular dichroism (CD) and magnetic circular dichroism spectra have been recorded for the Ca2+-Co2+ derivatives of the lentil (CCoLcH) and pea (CCoPSA) lectins (Co2+ at the S1 sites and Ca2+ at the S2 sites) and shown to be very similar for both proteins. The visible absorption and magnetic circular dichroism spectra indicate similar octahedral geometries for high spin Co2+ at S1 in both proteins, as found in the Ca2+-Co2+ complex of concanavalin A (CCoPL) (Richardson, C. E., and Behnke, W. D. (1976) J. Mol. Biol. 102, 441-451). The visible CD data, however, indicate differences in the environment around S1 of CCoLcH and CCoPSA compared to CCoPL. 1H NMR spectra at 90 MHz of the Co2+ and Ni2+ derivatives of the lectins show a number of isotropically shifted signals which arise from protons in the immediate vicinity of the S1 sites. Analysis of the spectra of the Co2+ derivatives in H2O and D2O has permitted resonance assignments of the side chain ring protons of the coordinated histidine at S1 in the lectins. Differences are observed in the H-D exchange rate of the histidine NH proton at S1 in concanavalin A compared to the lentil and pea lectins. NMR data of the Ni2+-substituted proteins, together with spectra of the Co2+ derivatives, also indicate that the side chains of a carboxylate ligand and of the histidine residue at S1 are positioned differently in concanavalin A than in the other two lectins. These results appear to account, in part, for the differences observed in the visible CD spectra of the Co2+-substituted proteins. In addition, binding of monosaccharides does not significantly perturb the spectra of the lectins. An unusual feature in the 1H NMR spectra of all three Co2+-substituted lectins is the presence of two exchangeable downfield shifted resonances which appear to be associated with the two protons of a slowly exchanging water molecule coordinated to the Ca2+ ion at S2. T1 measurements of CCoLcH have provided an estimation of the distances from the Co2+ ion to these two protons of 3.7 and 4.0 A.

Original languageEnglish (US)
Pages (from-to)16985-16994
Number of pages10
JournalThe Journal of biological chemistry
Volume262
Issue number35
StatePublished - Dec 15 1987
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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    Bertini, I., Viezzoli, M. S., Luchinat, C., Stafford, E., Cardin, A. D., Behnke, W. D., Bhattacharyya, L., & Brewer, C. F. (1987). Circular dichroism and 1H NMR studies of Co2+- and Ni2+-substituted concanavalin A and the lentil and pea lectins. The Journal of biological chemistry, 262(35), 16985-16994.