INVESTIGADORES
ZORREGUIETA Angeles
artículos
Título:
RapA2 is a calcium-binding lectin composed of two highly conserved cadherin-like domains that specifically recognize Rhizobium leguminosarum acidic exopolysaccharides
Autor/es:
ABDIAN, P; CARAMELO, J.; AUSMEES, N.; ZORREGUIETA, A
Revista:
JOURNAL OF BIOLOGICAL CHEMISTRY
Editorial:
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
Referencias:
Año: 2013 vol. 288 p. 2893 - 2904
ISSN:
0021-9258
Resumen:
In silico analyses have revealed a conserved protein domain (CHDL)
widely present in bacteria that has significant structural similarity to
eukaryotic cadherins. A CHDL domain was shown to be present in RapA, a
protein that is involved in autoaggregation of Rhizobium cells, biofilm
formation, and adhesion to plant roots as shown by us and others.
Structural similarity to cadherins suggested calcium-dependent
oligomerization of CHDL domains as a mechanistic basis for RapA action.
Here we show by circular dichroism spectroscopy, light scattering,
isothermal titration calorimetry, and other methods that RapA2 from
Rhizobium leguminosarum indeed exhibits a cadherin-like β-sheet
conformation and that its proper folding and stability are dependent on
the binding of one calcium ion per protein molecule. By further in
silico analysis we also reveal that RapA2 consists of two CHDL domains
and expand the range of CHDL-containing proteins in bacteria and
archaea. However, light scattering assays at various concentrations of
added calcium revealed that RapA2 formed neither homo-oligomers nor
hetero-oligomers with RapB (a distinct CHDL protein), indicating that
RapA2 does not mediate cellular interactions through a cadherin-like
mechanism. Instead, we demonstrate that RapA2 interacts specifically
with the acidic exopolysaccharides (EPSs) produced by R. leguminosarum
in a calcium-dependent manner, sustaining a role of these proteins in
the development of the biofilm matrix made of EPS. Because EPS binding
by RapA2 can only be attributed to its two CHDL domains, we propose that
RapA2 is a calcium-dependent lectin and that CHDL domains in various
bacterial and archaeal proteins confer carbohydrate binding activity to
these proteins.