Interdomain Ca(2+) effects in Escherichia coli alpha-haemolysin: Ca(2+) binding to the C-terminal domain stabilizes both C- and N-terminal domains

TY - JOUR

T1 - Interdomain Ca(2+) effects in Escherichia coli alpha-haemolysin

T2 - Ca(2+) binding to the C-terminal domain stabilizes both C- and N-terminal domains

AU - Sánchez-Magraner, Lissete

AU - Cortajarena, Aitziber L

AU - García-Pacios, Marcos

AU - Arrondo, José-Luis R

AU - Agirre, Jon

AU - Guérin, Diego M A

AU - Goñi, Félix M

AU - Ostolaza, Helena

PY - 2010/6

Y1 - 2010/6

N2 - alpha-Haemolysin (HlyA) is a toxin secreted by pathogenic Escherichia coli, whose lytic activity requires submillimolar Ca(2+) concentrations. Previous studies have shown that Ca(2+) binds within the Asp and Gly rich C-terminal nonapeptide repeat domain (NRD) in HlyA. The presence of the NRD puts HlyA in the RTX (Repeats in Toxin) family of proteins. We tested the stability of the whole protein, the amphipathic helix domain and the NRD, in both the presence and absence of Ca(2+) using native HlyA, a truncated form of HlyADeltaN601 representing the C-terminal domain, and a novel mutant HlyA W914A whose intrinsic fluorescence indicates changes in the N-terminal domain. Fluorescence and infrared spectroscopy, tryptic digestion, and urea denaturation techniques concur in showing that calcium binding to the repeat domain of alpha-haemolysin stabilizes and compacts both the NRD and the N-terminal domains of HlyA. The stabilization of the N-terminus through Ca(2+) binding to the C-terminus reveals long-range inter-domain structural effects. Considering that RTX proteins consist, in general, of a Ca(2+)-binding NRD and separate function-specific domains, the long-range stabilizing effects of Ca(2+) in HlyA may well be common to other members of this family.

AB - alpha-Haemolysin (HlyA) is a toxin secreted by pathogenic Escherichia coli, whose lytic activity requires submillimolar Ca(2+) concentrations. Previous studies have shown that Ca(2+) binds within the Asp and Gly rich C-terminal nonapeptide repeat domain (NRD) in HlyA. The presence of the NRD puts HlyA in the RTX (Repeats in Toxin) family of proteins. We tested the stability of the whole protein, the amphipathic helix domain and the NRD, in both the presence and absence of Ca(2+) using native HlyA, a truncated form of HlyADeltaN601 representing the C-terminal domain, and a novel mutant HlyA W914A whose intrinsic fluorescence indicates changes in the N-terminal domain. Fluorescence and infrared spectroscopy, tryptic digestion, and urea denaturation techniques concur in showing that calcium binding to the repeat domain of alpha-haemolysin stabilizes and compacts both the NRD and the N-terminal domains of HlyA. The stabilization of the N-terminus through Ca(2+) binding to the C-terminus reveals long-range inter-domain structural effects. Considering that RTX proteins consist, in general, of a Ca(2+)-binding NRD and separate function-specific domains, the long-range stabilizing effects of Ca(2+) in HlyA may well be common to other members of this family.

KW - Amino Acid Substitution

KW - Calcium

KW - Escherichia coli

KW - Escherichia coli Proteins

KW - Hemolysin Proteins

KW - Mutation, Missense

KW - Protein Binding

KW - Protein Stability

KW - Protein Structure, Tertiary

U2 - 10.1016/j.bbamem.2010.03.007

DO - 10.1016/j.bbamem.2010.03.007

M3 - Article

C2 - 20223223

SN - 0005-2736

VL - 1798

SP - 1225

EP - 1233

JO - Biochimica et biophysica acta-Biomembranes

JF - Biochimica et biophysica acta-Biomembranes

IS - 6

ER -