Rubber particle proteins, HbREF and HbSRPP, interact differently with lipids extracted from RRIM600 H. brasiliensis latex

Latex tapped from Hevea brasiliensis (rubber tree) contains rubber particles dispersed in C-serum. The spherical Hevea rubber particle can be described as a core of polymer surrounded by a biological membrane made of lipids and proteins. While it is agreed that the particle is made of an hydrophobic core of poly(cis-1,4-isoprene), the structure and composition of its lipid-protein surface membrane is still controversial [1-3]. Two major proteins are abundant at the surface of Hevea rubber particles namely, the rubber elongation factor (HbREF) and the small rubber particle protein (HbSRPP), which are mainly located at the surface of large rubber particles and small rubber particles, respectively [4]. Lipids extracted from rubber particles include phospholipids (PL), glycolipids (GL) and neutral lipids (NL) [5]. Recently, an approach in Langmuir films was applied to study the interactions of recombinant REF and SRPP with synthetic lipids (DMPC and asolectin) [6]. In the present study, we used surface pressure kinetics, ellipsometry, Brewster angle microscopy and polarization-modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS) to investigate the interactions between recombinant REF and SRPP with native lipids extracted and purified from Hevea RRIM600 latex collected in the Chanthaburi province, Thailand. Monolayers of native phospholipids, glycolipids and neutral lipids were successfully formed at the air-water interface. Pure lipid (PL, GL or NL) and mixed lipid-protein Langmuir monolayers were studied. The interactions between REF and SRPP with lipids are completely different. SRPP interacts mostly in surface with all types of lipids (PL, GL or NL), without modification of its secondary structure. In contrast REF inserts deeply in the lipid monolayer with all lipid classes. When it interacts with NL, REF is able to switch from a conformation in a-helices to b-sheet structures, as in its aggregated form (amyloid form) [7]. Interactions between REF and NL may have specific role in the plugging of rubber particles. (Texte intégral)