Vaccine 30 (2012) 1583–1593 Contents lists available at SciVerse ScienceDirect Vaccine jou rn al h om epa ge: www.elsevier.com/locate/vaccine Geographic differentiation of polymorphism in the Plasmodium falciparum malaria vaccine candidate gene SERA5 Kazuyuki Tanabe a,b,∗ , Nobuko Arisue b , Nirianne M.Q. Palacpac b,c , Masanori Yagi b , Takahiro Tougan b , Hajime Honma a,b , Marcelo U. Ferreira d , Anna Färnert e , Anders Björkman e , Akira Kaneko f,g , Masatoshi Nakamura h , Kenji Hirayama i , Toshihiro Mita j , Toshihiro Horii b,∗∗ a Laboratory of Malariology, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871, Japan b Department of Molecular Protozoology, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871, Japan c The Research Foundation for Microbial Diseases of Osaka University, Suita, Osaka 565-0871, Japan d Department of Parasitology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil e Infectious Diseases Unit, Department of Medicine Solna, Karolinska Institutet, 17176 Stockholm, Sweden f Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden g Department of Parasitology, Osaka City University Graduate School of Medicine, Osaka, Japan h Department of Tropical Medicine and Parasitology, Dokkyo Medical University, Tochigi 321-0293, Japan i Department of Immunogenetics, Global COE, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki 852-8523, Japan j Department of International Affairs and Tropical Medicine, Tokyo Women’s Medical University, Tokyo 162-8666, Japan a r t i c l e i n f o Article history: Received 17 October 2011 Received in revised form 20 December 2011 Accepted 23 December 2011 Available online 9 January 2012 Keywords: Malaria SERA5 Plasmodium falciparum Vaccine Polymorphism Geographical differentiation a b s t r a c t SERA5 is regarded as a promising malaria vaccine candidate of the most virulent human malaria para- site Plasmodium falciparum. SERA5 is a 120 kDa abundantly expressed blood-stage protein containing a papain-like protease. Since substantial polymorphism in blood-stage vaccine candidates may potentially limit their efficacy, it is imperative to fully investigate polymorphism of the SERA5 gene (sera5). In this study, we performed evolutionary and population genetic analysis of sera5. The level of inter-species divergence (kS = 0.076) between P. falciparum and Plasmodium reichenowi, a closely related chimpanzee malaria parasite is comparable to that of housekeeping protein genes. A signature of purifying selection was detected in the proenzyme and enzyme domains. Analysis of 445 near full-length P. falciparum sera5 sequences from nine countries in Africa, Southeast Asia, Oceania and South America revealed extensive variations in the number of octamer repeat (OR) and serine repeat (SR) regions as well as substantial level of single nucleotide polymorphism (SNP) in non-repeat regions (2562 bp). Remarkably, a 14 amino acid sequence of SERA5 (amino acids 59–72) that is known to be the in vitro target of parasite growth inhibitory antibodies was found to be perfectly conserved in all 445 worldwide isolates of P. falciparum evaluated. Unlike other major vaccine target antigen genes such as merozoite surface protein-1, apical membrane antigen-1 or circumsporozoite protein, no strong evidence for positive selection was detected for SNPs in the non-repeat regions of sera5. A biased geographical distribution was observed in SNPs as well as in the haplotypes of the sera5 OR and SR regions. In Africa, OR- and SR-haplotypes with low frequency (<5%) and SNPs with minor allele frequency (<5%) were abundant and were mostly continent- specific. Consistently, significant genetic differentiation, assessed by the Wright’s fixation index (Fst) of inter-population variance in allele frequencies, was detected for SNPs and both OR- and SR-haplotypes among almost all parasite populations. The exception was parasite populations between Tanzania and Ghana, suggesting frequent gene flow in Africa. The present study points to the importance of investi- gating whether biased geographical distribution for SNPs and repeat variants in the OR and SR regions affect the reactivity of human serum antibodies to variants. © 2011 Elsevier Ltd. All rights reserved. ∗ Corresponding author. Present address: Department of Molecular Protozoology, Research Institute for Microbial Diseases, 3-1 Yamada-oka, Suita, Osaka University, Osaka 565-0871, Japan. Tel.: +81 6 6879 8279; fax: +81 6 6879 8281. ∗∗ Corresponding author at: Department of Molecular Protozoology, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamada-Oka, Suita, Osaka 565-0871, Japan. Tel.: +81 6 6879 8279; fax: +81 6 6879 8281. E-mail addresses: kztanabe@biken.osaka-u.ac.jp (K. Tanabe), arisue@biken.osaka-u.ac.jp (N. Arisue), nirian@biken.osaka-u.ac.jp (N.M.Q. Palacpac), masanory@biken.osaka-u.ac.jp (M. Yagi), ttougan@biken.osaka-u.ac.jp (T. Tougan), homma@biken.osaka-u.ac.jp (H. Honma), muferrei@usp.br (M.U. Ferreira), Anna.Farnert@ki.se (A. Färnert), anders.bjorkman@karolinska.se (A. Björkman), akirakaneko555@gmail.com (A. Kaneko), nakamuram8823@citrus.ocn.ne.jp (M. Nakamura), hiraken@nagasaki-u.ac.jp (K. Hirayama), hiro-tm@research.twmu.ac.jp (T. Mita), horii@biken.osaka-u.ac.jp (T. Horii). 0264-410X/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.vaccine.2011.12.124