title: Genetic diversity of the merozoite surface protein-3 gene in Plasmodium falciparum populations in Thailand.
abstract: BACKGROUND
  An effective malaria vaccine is an urgently needed tool to fight against human malaria, the most deadly parasitic disease of humans. One promising candidate is the merozoite surface protein-3 (MSP-3) of Plasmodium falciparum. This antigenic protein, encoded by the merozoite surface protein (msp-3) gene, is polymorphic and classified according to size into the two allelic types of K1 and 3D7. A recent study revealed that both the K1 and 3D7 alleles co-circulated within P. falciparum populations in Thailand, but the extent of the sequence diversity and variation within each allelic type remains largely unknown.
  
  
  METHODS
  The msp-3 gene was sequenced from 59 P. falciparum samples collected from five endemic areas (Mae Hong Son, Kanchanaburi, Ranong, Trat and Ubon Ratchathani) in Thailand and analysed for nucleotide sequence diversity, haplotype diversity and deduced amino acid sequence diversity. The gene was also subject to population genetic analysis (Fst) and neutrality tests (Tajima's D, Fu and Li D* and Fu and Li' F* tests) to determine any signature of selection.
  
  
  RESULTS
  The sequence analyses revealed eight unique DNA haplotypes and seven amino acid sequence variants, with a haplotype and nucleotide diversity of 0.828 and 0.049, respectively. Neutrality tests indicated that the polymorphism detected in the alanine heptad repeat region of MSP-3 was maintained by positive diversifying selection, suggesting its role as a potential target of protective immune responses and supporting its role as a vaccine candidate. Comparison of MSP-3 variants among parasite populations in Thailand, India and Nigeria also inferred a close genetic relationship between P. falciparum populations in Asia.
  
  
  CONCLUSIONS
  This study revealed the extent of the msp-3 gene diversity in P. falciparum in Thailand, providing the fundamental basis for the better design of future blood stage malaria vaccines against P. falciparum.
authors: Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand.
authors: Sittiporn
authors: S
authors: Pattaradilokrat
authors: Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand.
authors: Vorthon
authors: V
authors: Sawaswong
authors: Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand.
authors: Phumin
authors: P
authors: Simpalipan
authors: Department of Pathology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, 10330, Thailand.
authors: Morakot
authors: M
authors: Kaewthamasorn
authors: College of Public Health Sciences, Chulalongkorn University, Bangkok, 10330, Thailand.
authors: Napaporn
authors: N
authors: Siripoon
authors: Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand. HPongchai@gmail.com.
authors: Pongchai
authors: P
authors: Harnyuttanakorn
mesh_terms: D000953:Antigens, Protozoan / Q000235:genetics*; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics; D014644:Genetic Variation; D006801:Humans; D010963:Plasmodium falciparum / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*; D015800:Protozoan Proteins / Q000235:genetics*; D017422:Sequence Analysis, DNA; D013785:Thailand
chemical_list: D000953:Antigens, Protozoan; D016054:DNA, Protozoan; D015800:Protozoan Proteins; C089133:merozoite surface protein 3, Plasmodium
keywords: DNA sequencing; Genetic diversity; Merozoite surface protein; Southeast Asia; Vaccine