Insights into the conformation and function of RapA2 a calcium-binding adhesion from Rhizobium leguminosarum

ABDIAN, P; CARAMELO, J.; RUSSO, D. M.; VOZZA, N; ZORREGUIETA, A

Puerto Madryin

Congreso; XLVI Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2010

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

R. leguminosarum develops a biofilm in minimal medium that depends on the acidic exopolysaccharide (EPS) and proteins secreted by the PrsDE type I system. RapA1, a substrate of PrsDE, is a 25 kDa Ca2+ binding protein. It is composed of two homologous domains proposed as lectin domains that recognize the EPS. RapA1 was termed an adhesin since it can agglutinate rhizobial cells. Our aim was to characterize RapA2 from R.l. bv viciae strain 3841 and seek out its role in biofilm formation. We performed homology modelling of RapA2 and found structural similarity to eukaryotic cadherins, involved in Ca2+ dependant cellular interactions. This observation was confirmed analyzing RapA2 by CD spectroscopy. RapA2 is composed of b-sheet elements and its thermal stability relies on Ca2+ binding. Despite these similarities, we showed by light scattering that RapA2 is not able to dimerize, a property essential for cadherin adhesive activity. Overexpression of homologous RapA1 in strain 3841 disrupted tight cell-cell interactions within the biofilm, which argues against a role in adhesion. Moreover, by means of a modified ELISA assay, we found that RapA2 interacts with the EPS indirectly by binding to EPS-associated proteins. Our results suggest that RapA2 may interact with other protein partners, forming complexes involved in the dynamics of the extracellular matrix of the biofilm.