A cholesterol consensus motif is required for efficient intracellular transport and raft association of a group 2 HA of influenza virus

The HA (haemagglutinin) of influenza viruses must be recruited to membrane rafts to perform its function in membrane fusion and virus budding. We previ-ously showed with Förster Resonance Energy Transfer (FRET) that deletion of the two rafttargeting features of HA, S-acylation at the cytoplasmic tail and the hydrophobic amino acids VIL in the outer part of the transmembrane region (TMR) lead to reduced raft association. In addition, exchange of VIL, but not of the S-acylation sites severely retards transport of HA through the Golgi. Here we have further characterized the ill-defined signal in the TMR. A sequence comparison suggests that leucine of VIL might be part of a cholesterol consensus motif (CCM) that is known to bind cholesterol to 7-TM-receptors. The signal also comprises a lysine and a tryptophan on one and a tyrosine on another TMR-helix and is conserved in group 2 HAs. Mutations in the CCM retard Golgi-localized processing of HA, such as acquisition of Endo-H resistant carbohydrates in the medial-Golgi and proteolytic cleavage in the TGN. The delay in transport of HA to and from the medial Golgi varied with the mutation suggesting that different transport steps are affected. All mutants analyzed by FRET also showed reduced association with rafts at the plasma membrane. Thus, the raft targeting signal of HA encompasses not only hydrophobic, but also aromatic and positively charged residues. We speculate that binding to cholesterol might facilitate intracellu...
Source: BJ Disease - Category: Biochemistry Authors: Tags: BJ Biomolecules Source Type: research