Plasmodium vivax represents the second most prevalent malaria species of major public health importance and the global eradication of malaria requires the development of vaccines to prevent infection. The lack of in vitro culture and a suitable animal model for P. vivax malaria are the major problems for the delay in developing a functional vivax vaccine. A number of antigens have been identified for P. vivax as potential malaria vaccine candidates and among these 42 kDa fragment of merozoite surface protein-1 (MSP-1(42)) is one of most promising antigen of asexual blood stage. In most of the earlier studies, the MSP-1(42) of malaria parasites was expressed as insoluble protein in inclusion bodies and it is difficult to get purified protein in conformation form. In the present study, we have cloned, overexpressed and characterized the 42 kDa fragment of P. vivax MSP-1 as soluble protein in Escherichia coli. The 42 kDa gene fragment of P. vivax MSP-1 was PCR amplified using specific primers, sequenced and subcloned into pTriEx-4 expression vector. The optimum expression of recombinant P. vivax protein was obtained in SOC growth medium by inducing with 0.2 mM IPTG at 37 degrees C for 4 h. The SDS-PAGE analysis showed a fusion protein of 55 kDa and about 80% was present in soluble form. The purified P. vivax MSP-1(42) was characterized and found to be correctly folded and in conformation form as evident by CD spectroscopy, presence of I free -SH group and the reactivity with reduction sensitive conformational monoclonals against P. vivax MSP-1(42). (C) 2014 Elsevier Inc. All rights reserved.