來(lái)自哈佛醫(yī)學(xué)院,，波士頓兒童醫(yī)院的研究人員發(fā)表了題為“Shape change in the receptor for gliding motility in Plasmodium sporozoites”的文章,，完成了瘧疾發(fā)生的重要表面蛋白的結(jié)構(gòu)測(cè)定,，并從中獲得了功能啟示。這項(xiàng)研究發(fā)表在《美國(guó)國(guó)家科學(xué)院院刊》（PNAS）雜志上,。

文章的第一作者為哈佛醫(yī)學(xué)院宋高潔博士，目前在哈佛醫(yī)學(xué)院從事博士后研究,。

瘧疾是一種由瘧原蟲(chóng)造成,，通過(guò)瘧蚊傳播的全球性寄生蟲(chóng)傳染病。瘧疾仍然是全球主要的傳染病和健康殺手之一,，每年因患瘧疾而死亡的人數(shù)達(dá)上百萬(wàn),。由于瘧疾的生活周期極其復(fù)雜，致使其疫苗研發(fā)也變得困難,。

TRAP蛋白是瘧原蟲(chóng)孢子體穿梭和入侵肝細(xì)胞的核心元件,，其通過(guò)胞外結(jié)構(gòu)域連接細(xì)胞或基質(zhì)的表面受體，并通過(guò)胞內(nèi)區(qū)與孢子體內(nèi)馬達(dá)蛋白聯(lián)系,，從而介導(dǎo)孢子體的遷移,因此是重要的疫苗研究靶點(diǎn),。但由于目前TRAP蛋白的三維結(jié)構(gòu)并不清楚，疫苗研發(fā)科學(xué)家只能工作在“黑暗”中,。

在這篇文章中,，基于X-射線衍射技術(shù)，研究人員解析了TRAP蛋白的胞外區(qū)的晶體結(jié)構(gòu)，并發(fā)現(xiàn)TRAP的胞外區(qū)VWA結(jié)構(gòu)域存在兩種構(gòu)型（分別稱“開(kāi)放”或“閉合”）,。

在兩種構(gòu)型中,，VWA結(jié)構(gòu)域與TSR結(jié)構(gòu)域相對(duì)位置發(fā)生非常顯著的變化：開(kāi)放構(gòu)型中，整個(gè)分子呈伸展?fàn)?，并產(chǎn)生一個(gè)新的由一對(duì)反平行β片組成的結(jié)構(gòu)域（研究人員將其命名為“彈性飄帶區(qū)”）,。這段新的結(jié)構(gòu)域，可能是新的疫苗或抗體研究的靶點(diǎn),。TRAP的三維結(jié)構(gòu)的解析,，有助于我們理解孢子體穿梭及瘧疾發(fā)生的機(jī)理，并為疫苗研發(fā)打下堅(jiān)實(shí)基礎(chǔ),。(生物谷Bioon.com)

doi: 10.1073/pnas.1218581109
PMC:
PMID:
Shape change in the receptor for gliding motility in Plasmodium sporozoites

Gaojie Song, Adem C. Koksal, Chafen Lu, and Timothy A. Springer1

Sporozoite gliding motility and invasion of mosquito and vertebrate host cells in malaria is mediated by thrombospondin repeat anonymous protein (TRAP). Tandem von Willebrand factor A (VWA) and thrombospondin type I repeat (TSR) domains in TRAP connect through proline-rich stalk, transmembrane, and cytoplasmic domains to the parasite actin-dependent motility apparatus. We crystallized fragments containing the VWA and TSR domains from Plasmodium vivax and Plasmodium falciparum in different crystal lattices. TRAP VWA domains adopt closed and open conformations, and bind a Mg2+ ion at a metal ion–dependent adhesion site implicated in ligand binding. Metal ion coordination in the open state is identical to that seen in the open high-affinity state of integrin I domains. The closed VWA conformation associates with a disordered TSR domain. In contrast, the open VWA conformation crystallizes with an extensible β ribbon and ordered TSR domain. The extensible β ribbon is composed of disulfide-bonded segments N- and C-terminal to the VWA domain that are largely drawn out of the closed VWA domain in a 15 Å movement to the open conformation. The extensible β ribbon and TSR domain overlap at a conserved interface. The VWA, extensible β ribbon, and TSR domains adopt a highly elongated overall orientation that would be stabilized by tensile force exerted across a ligand-receptor complex by the actin motility apparatus of the sporozoite. Our results provide insights into regulation of “stick-and-slip” parasite motility and for development of sporozoite subunit vaccines. Mosquitoes transmit malaria to humans via sporozoites. Sporozoites are important targets of pre-erythrocytic malaria vaccines. However, we know little about the structure and arrangement of the two most important vaccine targets on sporozoite surfaces, the circumsporozoite (CS) protein (1⇓–3) and thrombospondin repeat anonymous protein (TRAP) (4, 5). CS is a constitutive sporozoite surface protein and has a glycophosphatidylinositol anchor. TRAP mediates sporozoite gliding motility and cell invasion in both mosquito and vertebrate hosts (6). TRAP is mobilized from micronemes to the plasma membrane at the apical end of sporozoites, and is translocated to the posterior end during cell migration and invasion (7, 8). TRAP spans the plasma membrane, and its cytoplasmic domain connects to the actin cytoskeleton through aldolase, permitting functional cooperation between extracellular adhesive domains and the intracellular actin/myosin motor (8⇓–10). The TRAP ectodomain contains tandem von Willebrand factor A (VWA) and thrombospondin repeat (TSR) domains. A subset of VWA domains, including the inserted (I) domains in integrins, contain metal ion-dependent adhesion sites (MIDAS), with a Mg2+ ion at the center of the ligand binding site (11). Conformational change transmitted from neighboring domains regulates affinity of I domains for ligand. The TRAP VWA domain contains the sequence signature of a MIDAS. Mutations of putative TRAP VWA domain MIDAS residues and deletion of a segment of the TRAP TSR domain disrupt gliding motility and invasion of mosquito salivary glands and mammalian liver cells (12, 13). A crystal structure of a fragment of the von Willebrand factor A (VWA) domain from a Toxoplasma gondii TRAP orthologue, micronemal protein-2 (MIC-2) (5), and an NMR structure of the TRAP TSR domain (4) did not yield insights into conformational regulation or how these neighboring domains might interact in TRAP or MIC-2. In integrins, induction of the high-affinity, open conformation of both the α- and β-subunit I domains is relayed between tandem domains by axial displacement of the C-terminal α helix (14). We hypothesized that the TRAP VWA domain would undergo conformational change during ligand binding, induced by tensile force transmitted through the TSR domain by the motility apparatus. To test this hypothesis, we crystallized TRAP in multiple lattices and conformational states.