A 46000 dalton Plasmodium falciparum merozoite surface glycoprotein not related to the 185000?195000 dalton schizont precursor molecule: isolation and characterization

Abstract

A 46,000 dalton glycoprotein was isolated by extraction of freshly harvested P. falciparum merozoites (FCB1 strain), followed by gel electrophoresis of the extract and electroelution. The antigen is present in the late ring, trophozoite, schizont, and segmenter stages and is localized on the merozoite surface at the end of schizogony. It is not related to the 185,000-195,000 dalton schizont antigen. An antiserum against the 46,000 dalton antigen inhibits invasion of erythrocytes by merozoites. The isolated antigen is identical to the antigen against which monoclonal antibody (mcab) 13.4 is directed.

Plasmodium falciparum merozoite surface protein 2 is unstructured and forms amyloid-like fibrils

“…N-terminal proteolytic processing of MSP2 (other than removal of the secretion signal) has not been observed (Fig. S7) but attempts by us (data not shown) and others [66] to identify the N-terminus of the mature MSP2 polypeptide have failed because the N-terminus was blocked.…”

Transcription of the gene for the merozoite surface antigen MSA2 of the human malaria parasite Plasmodium falciparum during the asexual cycle

“…'osylated M$A2 (46K). (iii) As the natund MgA2 is one of the mt~jor schizont and mcrozoit¢ proteins [6], so 43K is also among the major polypeptides encoded by late mRNAs (see in Fig, I tracks for mRNAs from 37, 42 and 47 h). (iv) The 43K polypcptide must contain some of those palm, site epitopcs that come into contact with the host immune system during the natural inf~tion because 43K was precipitated by a pool of human immune sera, but not by a truman non-immune serum (data not shown).…”

“…The merozoite surfitcc protein MSA2 is a polymorphic antigen with an apparent r~lative molecular weight (M,) vaD'ing among different strains: this antigen is being considered Ibr the development oi'a malaria vaccine because it is expressed on the parasite surface and antibodies against it block the invasion [I-1 I]. MSA2 has been demonstrated in trophozoites, schizonts, segmenters and isolated merozoites by several techniques: using either poly-or monotional antibodies the protein was detect~t by imnmnoblotting [1,7] and immunopr~-cipitation of extracts from synchronous cultures [6,91,, ~md b~ IFA [1,9]. In the ring stages low MSA2 levels could be det~ted by immunoprccipitation [6] and immunoblotting [9] or,xtraeis t-~m synchronous cultures using polyclonai antibodies.…”

“…MSA2 has been demonstrated in trophozoites, schizonts, segmenters and isolated merozoites by several techniques: using either poly-or monotional antibodies the protein was detect~t by imnmnoblotting [1,7] and immunopr~-cipitation of extracts from synchronous cultures [6,91,, ~md b~ IFA [1,9]. In the ring stages low MSA2 levels could be det~ted by immunoprccipitation [6] and immunoblotting [9] or,xtraeis t-~m synchronous cultures using polyclonai antibodies. Howcver, no antigen could be detected in rings by using single monoclona[ antibodies in IFA [I], immunoblotting o£ extn~cts from ring Abbrc~'ia;ions: {buffers used tbr immunop~'cipitation) T, 50 mM "rris.CI {pH S,0); E, 5 mM ED'i'-~ (pH 8,0): N, 0,5 M NaCl; Z, 5 mM Zwittergent 3-12 (Caibiochem-Behring~: A, I mg/ml bovine serum albumin: i, mix ofprotease inhibitors (2% aprotinin (Bayer): antipain, bcstatin and pcpstatin A (Sibm~a), each at I/Jglml: 2 mM phenylmethylsulphonyl fluoride (BDH)).…”

Isolation and functional characterization of Plasmodium falciparum merozoite antigens

“…The serum against another antigen, the 46 kDa merozoite surface antigen (which is not derived from the high molecular weight precursor, but is rather a protein syn-",hesised at the trophozoite stage and which is not processed during the schizogony cycle [17,40]) is recognised by the corresponding immune serum as a single band (Fig. 6).…”