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We have identified a single tryptophan (Trp) residue responsible for loss of binding and biological activity upon ultraviolet (UV) light irradiation in MEDI-493, a humanized monoclonal antibody (MAb) against respiratory syncytial virus (RSV). This finding provides a better understanding of structure-function relationship in a 150-kDa protein. Irradiation of MEDI-493 with UV light resulted in spectral changes typical of Trp photoproducts and in a progressive loss of MEDI-493 binding and biological activity as measured by ELISA, Biacore, and cell-based assays. Mass spectrometric characterization of the proteolytic peptides generated from the UV irradiated MEDI-493 confirmed that most methionine (Met) and a few Trp residues were oxidized to various extents upon exposure to UV light. Among Trp residues, only Trp-105, containing the most solvent-exposed indole moiety in MEDI-493 and residing in a complementary-determining region (CDR) of the heavy chain, was significantly oxidized. When bound to a synthetic antigenic peptide, MEDI-493 showed significant resistance toward binding activity loss during UV irradiation. A second MAb (MEDI-524) with Trp-105 replaced by phenylalanine (Phe) showed a similar pattern of Met oxidation, but no loss of binding and biological activity following irradiation. Treatment of both MAbs with Met- and Trp-specific oxidizing reagents showed that oxidation of Trp-105 correlated with the activity loss, whereas Met oxidation did not affect the activity. These results demonstrate that Trp-105 in MEDI-493 is responsible for the UV light-induced effects.

Respiratory syncytial virus (RSV) matrix (M) nuclear import for the first time, showing that M is able to localize in the nucleus in the absence of other RSV gene products, through M amino acids 110-183 is examined. The M protein of RSV plays an important role in virus assembly through specific interactions with RSV nucleocapsids and envelope glycoproteins in the cytoplasm as well as with the host cell membrane.

A 13-residue peptide sequence from a respiratory syncitial virus fusion protein is constrained in an alpha-helical conformation by fusing two back-to-back cyclic alpha-turn mimetics. The resulting compound displays potent activity in both a recombinant fusion assay and an RSV antiviral assay, and demonstrates for the first time that back-to-back modular alpha-helix mimetics can produce functional antagonists of important protein-protein interactions.