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Published on: November 10, 2015
Analysis of polymorphisms and selective pressures on ama1 gene in Plasmodium knowlesi isolates from Sabah, Malaysia
Chuen Yang Chua1, Ping Chin Lee, Tiek Ying Lau
1Biotechnology Research Institute, Universiti Malaysia Sabah, 88400 Kota Kinabalu, Sabah, Malaysia. sophialau@ums.edu.my.
Abstract:
The apical membrane antigen-1 (AMA-1) of Plasmodium spp. is a merozoite surface antigen that is essential for the recognition and invasion of erythrocytes. Polymorphisms occurring in this surface antigen will cause major obstacles in developing effective malaria vaccines based on AMA-1. The objective of this study was to characterize ama1 gene in Plasmodium knowlesi isolates from Sabah. DNA was extracted from blood samples collected from Keningau, Kota Kinabalu and Kudat. The Pkama1 gene was amplified using nested PCR and subjected to bidirectional sequencing. Analysis of DNA sequence revealed that most of the nucleotide polymorphisms were synonymous and concentrated in domain I of PkAMA-1. Forteen haplotypes were identified based on amino acid variations and haplotype K5 was the most common haplotype. dN/dS ratios implied that purifying selection was prevalent in Pkama1 gene. Fu and Li's D and F values further provided evidence of negative selection acting on domain II of Pkama1. Lownucleotide diversitywas also detected for the Pkama1 sequences,which is similar to reports on Pkama1 from Peninsular Malaysia and Sarawak. The presence of purifying selection and low nucleotide diversity indicated that domain II of Pkama1 can be used as a target for vaccine development.
Insights
Polymorphisms in Plasmodium knowlesi's apical membrane antigen-1 (AMA-1) pose challenges for malaria vaccine development. However, domain II of AMA-1 shows low diversity and purifying selection, suggesting its potential as a vaccine target.
Area of Science:
- Malariology
- Molecular Biology
- Vaccine Development
Background:
- Apical membrane antigen-1 (AMA-1) is crucial for Plasmodium merozoite invasion of erythrocytes.
- Polymorphisms in AMA-1 present significant hurdles for developing effective malaria vaccines.
Purpose of the Study:
- To characterize the ama1 gene in Plasmodium knowlesi isolates from Sabah.
- To assess the potential of PkAMA-1 domains for malaria vaccine development.
Main Methods:
- DNA extraction from blood samples from Sabah.
- Nested PCR amplification and bidirectional sequencing of the Pkama1 gene.
- Analysis of nucleotide polymorphisms, haplotype identification, and selection pressure (dN/dS ratios, Fu and Li's D and F tests).
Main Results:
- Most nucleotide polymorphisms in Pkama1 were synonymous and located in domain I.
- Fourteen haplotypes were identified, with K5 being the most common.
- Purifying and negative selection were prevalent in Pkama1, particularly in domain II, with low overall nucleotide diversity.
Conclusions:
- Domain II of PkAMA-1 exhibits low nucleotide diversity and evidence of purifying selection.
- These characteristics suggest that domain II of PkAMA-1 is a promising target for malaria vaccine development.
