This is the C-terminal domain, also known as the beta domain, of Rubsico Assembly Chaperone protein (Raf1). Raf1 is necessary for rubisco to catalyze the rate-limiting step of carbon fixation through carboxylating the five-carbon sugar substrate ribulose-1,5-bisphosphate. The beta domains primary function is dimerization, which is critical for Raf1 to achieve the necessary avidity for complex formation with RbcL (the large complex sub-unbit of Rubsico) assembly intermediates. The beta domain is also involved, to a small extent, in binding to RbcL with use of the lustiness near the beta domain's conserved top surface [1].

1: Structure and mechanism of the Rubisco-assembly chaperone Raf1. Hauser T, Bhat JY, Milicic G, Wendler P, Hartl FU, Bracher A, Hayer-Hartl M; Nat Struct Mol Biol. 2015;22:720-728. PMID:26237510