Question

7. Explain each class - proteins that govern merozoite invasion.

8. Summarize in 6 sentences, in your own word, the stages of invasion.

Answer 1

7. Merozoite proteins that governs merozoite invasion.

•Adhesins Localized to Micronemes

•EBA-175 (sialic binding protein of P. falciparum)

•Duffy-binding protein (P. vivax and P. knowlesi

TRAP family

•SSP2 (sporozoite surface protein-2) º TRAP (thrombospondin-related adhesive protein)

•Toxoplasma, Eimeria and Cryptosporidium proteins with homology to SSP2/TRAP

•CTRP, circumsporozoite- and TRAP-related protein (Plasmodium ookinete stage)

•Thrombospondin family characterized by von Willebrand factor type A domain. Functions in cell-cell and cell-matrix interactions.

Stages of invasion

1. Initial contact

2. Reorientation (Deformation):

accompanied by erythrocyte deformation

AMA-1 (Apical Membrane Antigen-1) implicated

•apical membrane antigen-1

•binds erythrocytes

•antibodies inhibit invasion and reorientation

•antibodies do not inhibit initial attachment

3. Junction formation:

•junction becomes an annulus (ring)

•Rhoptries also participate in junction formation

•Rhoptry neck proteins (RONs) inserted into host membrane

•RON2 interacts with AMA-1

•Forms part of the moving junction

•Highly conserved in Apicomplexa

•Force generation involves actin and unique Apicomplexan membrane associated myosin

4. Entry:

•clearance of erythrocyte membrane proteins

•host membrane invagination

•parasitophorous vacuolar membrane (PVM) formation

•discharge of rhoptries