Cap-binding activity of an eIF4E homolog from Leishmania.
All eukaryotic mRNAs possess a 5'-cap (m(7)GpppN) that is recognized by a family of cap-binding proteins. These participate in various processes, such as RNA transport and stabilization, as well as in assembly of the translation initiation complex. The 5'-cap of trypanosomatids is complex; in addition to 7-methyl guanosine, it includes unique modifications on the first four transcribed nucleotides, and is thus denoted cap-4. Here we analyze a cap-binding protein of Leishmania, in an attempt to understand the structural features that promote its binding to this unusual cap. LeishIF4E-1, a homolog of eIF4E, contains the conserved cap-binding pocket, similar to its mouse counterpart. The mouse eIF4E has a higher K(as) for all cap analogs tested, as compared with LeishIF4E-1. However, whereas the mouse eIF4E shows a fivefold higher affinity for m(7)GTP than for a chemically synthesized cap-4 structure, LeishIF4E-1 shows similar affinities for both ligands. A sequence alignment shows that LeishIF4E-1 lacks the region that parallels the C terminus in the murine eIF4E. Truncation of this region in the mouse protein reduces the difference that is observed between its binding to m(7)GTP and cap-4, prior to this deletion. We hypothesize that variations in the structure of LeishIF4E-1, possibly also the absence of a region that is homologous to the C terminus of the mouse protein, promote its ability to interact with the cap-4 structure. LeishIF4E-1 is distributed in the cytoplasm, but its function is not clear yet, because it cannot substitute the mammalian eIF4E in a rabbit reticulocyte in vitro translation system.
Yoffe
Yael
Y
Department of Life Sciences, Ben-Gurion University of the Negev, P.O.B. 653, Beer Sheva 84105, Israel.
Zuberek
Joanna
J
Lewdorowicz
Magdalena
M
Zeira
Ziv
Z
Keasar
Chen
C
Orr-Dahan
Irit
I
Jankowska-Anyszka
Marzena
M
Stepinski
Janusz
J
Darzynkiewicz
Edward
E
Shapira
Michal
M
D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D003198:Computer Simulation; D017124:Conserved Sequence; D003593:Cytoplasm / Q000737:chemistry; D039561:Eukaryotic Initiation Factor-4E / Q000737:chemistry / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D007891:Leishmania / Q000378:metabolism*; D018320:Leishmania major / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D039381:RNA Cap-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D016053:RNA, Protozoan / Q000302:isolation & purification / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D039561:Eukaryotic Initiation Factor-4E; D039381:RNA Cap-Binding Proteins; D016053:RNA, Protozoan; D011994:Recombinant Proteins; D006153:Guanosine Diphosphate