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Structural features of the combining site region of Erythrina corallodendron lectin: Role of tryptophan 135

journal contribution
posted on 2023-06-08, 05:02 authored by Rivka Adar, Ernesto Moreno, Hansjorg Streicher, Karl-Anders Karlsson, Jonas Angstrom, Nathan Sharon
The role of Trp 135 and Tyr 108 in the combining site of Erythrina corallodendron lectin (ECorL) was investigated by physicochemical characterization of mutants obtained by site-directed mutagenesis, hemagglutination-inhibitin studies, and molecular modeling, including dynamics simulations. The findings demonstrate that Trp 135 in ECorL: (1) is required for the tight binding of Ca2+ and Mn2+ to the lectin because mutation of this residue into alanine results in loss of these ions upon dialysis and concomitant reversible inactivation of the mutant; (2) contributes to the high affinity of methyl alpha-N-dansylgalactosaminide (Me alpha GalNDns) to the lectin; and (3) is solely responsible for the fluorescence energy transfer between the aromatic residues of the lectin and the dansyl group in the ECorL-Me alpha GalNDns complex. Docking of Me alpha GalNDns into the combining site of the lectin reveals that the dansyl moiety is parallel with the indole of Trp 135, as required for efficient fluorescence energy transfer, in one of the two possible conformations that this ligand assumes in the bound state. In the W135A mutant, which still binds Me alpha GalNDns strongly, the dansyl group may partially insert itself into the place formerly occupied by Trp 135, a process that from dynamics simulations does not appear to be energetically favored unless the loop containing this residue assumes an open conformation. However, a small fraction of the W135A molecules must be able to bind Me alpha GalNDns in order to explain the relatively high affinity, as compared to galactose, still remaining for this ligand. A model for the molecular events leading to inactivation of the W135A mutant upon demetallization is also presented in which the cis-trans isomerization of the Ala 88-Asp 89 peptide bond, observed in high-temperature dynamics simulations, appears not to be a required step.

History

Publication status

  • Published

Journal

Protein Science

ISSN

0961-8368

Publisher

Wiley-Blackwell

Issue

1

Volume

7

Page range

52-63

Department affiliated with

  • Chemistry Publications

Full text available

  • No

Peer reviewed?

  • Yes

Legacy Posted Date

2012-02-06

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