Crystal structure of Marburg virus VP24

Abstract

The VP24 protein plays an essential, albeit poorly understood role in the filovirus life cycle. VP24 is only 30% identical between Marburg virus and the ebolaviruses. Furthermore, VP24 from the ebolaviruses is immunosuppressive, while that of Marburg virus is not. The crystal structure of Marburg virus VP24, presented here, reveals that although the core is similar between the viral genera, Marburg VP24 is distinguished by a projecting β-shelf and an alternate conformation of the N-terminal polypeptide.

FIG 1

Overall architecture of Marburg virus VP24. (A to C) Faces 1 to 3 of the pyramidal VP24 structure are illustrated in rainbow coloring from the N terminus (navy blue) to the C terminus (red). The extended beta shelf formed by strands β17 and β18 is visible on the right of face 2 and the left of face 3. The descending N terminus of Marburg virus VP24 connects to the protein body via residues 13 to 20, which are disordered. (D) Topology diagram of Marburg virus VP24, with secondary structure elements sequentially numbered and colored from N to C as described for panels A to C. α-Helices are indicated by cylinders, and β-strands by arrows. Panels A to C were produced using Pymol (Delano Scientific) (34), and the topology diagram using Pro-origami (35).

FIG 2

Differences between Marburg virus and ebolavirus VP24s. (A) Marburg virus (MARV) and Sudan virus (SUDV) VP24 structures are superimposed and illustrated with face 3 oriented toward the viewer. Conformational differences in α13 between Marburg virus copy B and Sudan virus are highlighted with a black circle. The projecting β17-β18 shelf in Marburg virus is apparent on the left, and the position of the Marburg virus VP24 N terminus on the right. (B) Rotation of the superimposed structures so that differences in structure in β17-β18 are apparent. In the ebolaviruses, the equivalent residues do not make an extended shelf but instead form shorter strands connected by a loop/helical structure. (C) Marburg virus VP24 is illustrated in gray, oriented as described for panel A. VP24 residues conserved across the filovirus family (Marburg and five ebolaviruses) are colored dark blue; those visible in this view are labeled. Conservation in VP24 focuses on face 3, the N terminus, and the pocket at the base connecting faces 1 and 3. Figures were created using PyMol (Delano Scientific) (34).

FIG 3

(A) The top of the VP24 pyramids for Marburg virus copy A and copy B and the ebolaviruses (Sudan virus [SUDV] and Reston virus [RESTV]). Residues 142 to 146, which are thought to interact with karyopherin α1 in Ebola virus VP24, differ in sequence from the same residues in the nonimmunosuppressive Marburg virus VP24. Note, for example, the conserved placement of Arg 139/140, Asp 143, and Gln 144 in the two ebolaviruses. These positions are occupied by Asn 139, Ile 143, and Tyr 144 in Marburg virus. This site appears somewhat flexible in Marburg virus, as copies A and B of Marburg virus VP24 adopt different conformations. Copy B forms helix α13 with Tyr 144 rotated downward and Ile 143 upward, but copy A adopts a more extended structure with Tyr 144 rotated upward and Ile 143 downward. (B) Differences in conformation in residues 139 to 143 (α13) appear to be caused by crystal packing interactions. Illustrated here are the crystal packing interactions of copies A and B in the asymmetric unit. Note the alternate rotation of Tyr 144 between the two structures. (C) The N terminus of VP24 may be involved in VP24 oligomerization (33). In the crystal packing, the N termini of the two copies of Marburg virus VP24 reach across to bind into a shallow groove on the surface of the neighboring VP24.