Assessment and characterization of Ca2+-ATPase expression in selected isolates and clones of Plasmodium falciparum

Ca2+-ATPase expression in 15 selected isolates from malaria patients at the University College Hospital (UCH) Ibadan and two cloned strains (W2-chloroquine resistant, D6-chloroquine sensitive) of P.falciparum was assessed using spectrophotometric assay method. The kinetics of activity of Ca2+- ATPase in three isolates (NCP 14, NCP5, NCP1) and two clones (W2, D6) also assessed. 12% SDS-PAGE analysis of total proteins in one isolate (NCP14) and two clones (W2, D6) was also investigated. All the selected isolates and the two cloned strains exhibited measurable Ca2+-ATPase activity. The Ca2+-ATPase activity in cloned strain D6 (6.50 + 0.74mmolPi/min/mg protein) was higher than in cloned strain W2 (3.93 + 0.61mmolPi/min/mg protein. The Ca2+-ATPase activity in isolates from malaria patients varied widely (1.95 + 0.74 - 21.56 +1.43mmolPi/min/mg protein). The kinetic constants obtained for the two cloned strains showed that clone W2 had a higher Vmax (Vmax = 363mmolPi/min/mg protein) than clone D6 (Vmax = 74mmolPi/min/mg protein). All the isolates and the two cloned strains showed similar affinity for ATP (Km ~ 10mM). Scan of SDS-PAGE gel of total proteins in the isolate and cloned strains showed the presence of oligopeptide bands of molecular weights range of 148-176 kDa; 116-123 kDa respectively. These suggest the presence of predicted polypeptide of Ca2+-ATPase nature of molecular weight estimate of 139 kDa. The study agrees with previous findings that Ca2+-ATPase is functionally expressed in P.falciparum, The study also indicates that Ca2+-ATPase functional expression may vary with isolate or clone but the ATP binding mechanism to the enzyme is similar in all isolates and clones of P. falciparum. The study further suggests a possible association between acquisition of chloroquine resistance and Ca2+-ATPase functional expression in P. falciparum.