Abstract
The Baculoviridae family of viruses encode a viral Ubiquitin (vUb) gene. Though the vUb is homologous to the host eukaryotic Ubiquitin (Ub), its preservation in the viral genome indicates unique functions that are not compensated by the host Ub. We report the structural, biophysical, and biochemical properties of the vUb from Autographa californica multiple nucleo-polyhedrosis virus (AcMNPV). The packing of central helix α1 to the beta-sheet β1-β5 is different between vUb and Ub. Consequently, its stability is lower compared with Ub. However, the surface properties, ubiquitination activity, and the interaction with Ubiquitin-binding domains are similar between vUb and Ub. Interestingly, vUb forms atypical polyubiquitin chain linked by lysine at the 54th position (K54), and the deubiquitinating enzymes are ineffective against the K54-linked polyubiquitin chains. We propose that the modification of host/viral proteins with the K54-linked chains is an effective way selected by the virus to protect the vUb signal from host DeUbiquitinases.
Highlights
Ubiquitin (Ub), a 76 residue protein, regulates multiple cellular pathways and is a major way of regulating protein levels by the Ubiquitin-proteasome pathway [1,2,3]
Our study proposes that the virus encodes viral Ubiquitin (vUb) to conjugate substrates with the unique linkage of polyubiquitin chain
Sequence conservation of viral ubiquitin A gene tree was reconstructed using Maximum Likelihood method from all Ubiquitin coding amino-acid sequences taken from 39 baculoviruses, out of which 31 are Nucleo Polyhedrosis Virus (NPV) including Autographa Californica Multiple NucleoPolyhedrosis Virus (AcMNPV) and 8 are Granulovirus (GV) (Table S1)
Summary
Ubiquitin (Ub), a 76 residue protein, regulates multiple cellular pathways and is a major way of regulating protein levels by the Ubiquitin-proteasome pathway [1,2,3]. Ubiquitin is covalently attached to the target substrate via an isopeptide bond to generate a post-translation modification (PTM). At the end of conjugation, the C-terminal glycine residue of Ubiquitin forms an isopeptide bond with the ɛ-amino group of the substrate’s lysine residue. Ubiquitin can build polyubiquitin chains via seven lysine residues, and depending on chain linkage, the function of the polyUb chain is decided [4]. For e.g., a substrate with K63 polyUb chains is involved in DNA repair pathways [5] while K11 and K48 polyUb chains eliminate the substrate via proteasomal degradation [6]
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