Filovirus Entry: A Novelty in the Viral Fusion World

Hunt, Catherine L.; Lennemann, Nicholas J.; Maury, Wendy

Filovirus GP 2 is similar to other class I viral glycoproteins that mediate fusion events. GP 2 is composed of a fusion loop found near the amino terminus followed by a N-terminal heptad repeat region, a C-terminal heptad repeat region, a transmembrane region and a short cytoplasmic tail [6, 8, 9] . In the pre-fusion form on the surface of newly budded virions, the fusion loop and N-terminal heptad region are integral regions of the GP 1 /GP 2 trimeric structure, forming a platform or base upon which GP 1 sits ( Figure 1 ). In contrast, the C-terminal heptad repeat region in the pre-fusion form may contain little structure and was deleted in the crystallization studies and it is not thought to contribute to the metastable, pre-fusion form of GP [7] . Not surprisingly, both the fusion loop and N-terminal heptad repeat are conserved (>70% identity) between ZEBOV and the Musoke strain of MARV, but the remaining portions of GP 2 have limited identity. Site directed mutagenesis studies of EBOV or MARV GP 2 [14, [17] [18] [19] [20] [21] [22] [23] suggest a similar chain of events to those previously reported for other class I viral glycoproteins leads to viral/cell membrane fusion [6, 24, 25] . These events will be discussed in detail below.