Effects of calcium and protons on the secondary structure of the nodulation protein NodO from Rhizobium leguminosarum biovar viciae

Mauro Dalla Serra, J. Mark Sutton, Frank Höper, J. Alan Downie, Gianfranco Menestrina*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)

Abstract

NodO, a 30-kDa nodulation protein secreted by Rhizobium leguminosarum biovar viciae, belongs to a family of proteins produced by Gram-negative bacteria containing a variable number of glycine/aspartates nonapeptides. In some instances, these are organized into a parallel β-roll structure and bind Ca2+ (one ion per repeat). To gain insight into NodO's secondary and tertiary structures, and their dependence upon Ca2+ binding, we performed fluorescence experiments and FTIR spectroscopy. We found that calcium binds to the protein, promoting about a 10% increase in β-structure mainly to the expense of random-coil. Protons can also induce a reversible change in NodO structure, as indicated by quenching of intrinsic tryptophan fluorescence and binding of ANS, albeit probably via a different mechanism. Tb3+, a trivalent lanthanide, can compete with Ca2+ for the same binding sites, but with higher affinity. The number of Ca2+ binding sites, estimated by FTIR spectroscopy, was found to be consistent with the number of predicted repeats.

Original languageEnglish
Pages (from-to)516-522
Number of pages7
JournalBiochemical and Biophysical Research Communications
Volume263
Issue number2
DOIs
Publication statusPublished - 24 Sep 1999
Externally publishedYes

Bibliographical note

Funding Information:
This work was financially supported by the Italian Consiglio Na-zionale delle Ricerche (CNR), by the Istituto Trentino di Cultura (ITC), by a special grant from the Provincia Autonoma di Trento (PAT, 1913/CONV/1458), and by the British Biotechnology and Biological Sciences Research Council (BBSRC). MDS was the recipient of a fellowship from CNR (N° 201.02.45-21.02.05), FH was supported by a post-doctoral fellowship of the European Community (European Project CRHX-CT93-055), and JMS was employed on BBSRC Grant PG208/554.

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