UNASSIGNED: Virus-specific interaction between the attachment protein (HN) and the fusion protein (F) is prerequisite for the induction of membrane fusion by @entity15609 viruses. This HN-F interaction is presumably mediated by particular @entity1522 in the HN stalk domain and those in the F head domain. We found in the present study, however, that an SV41 F-specific chimeric @entity38545 HN protein, SCA, whose cytoplasmic, transmembrane, and stalk domains were derived from the SV41 HN protein, could not induce cell-cell fusion of BHK-21 cells when coexpressed with an SV41 HN-specific chimeric @entity38545 F protein, no. 36. Similarly, a headless form of the SV41 HN protein failed to induce fusion with chimera no. 36, whereas it was able to induce fusion with the SV41 F protein. Interestingly, substitution of 13 @entity1522 of the SCA head domain, that are located at or around the dimer interface of the head domain, with the SV41 HN counterparts resulted in a chimeric HN protein, SCA-RII, which induced fusion with chimera no. 36 but not with the SV41 F protein. More interestingly, retrosubstitution of 11 out of the 13 @entity1522 of SCA-RII with the SCA counterparts resulted in another chimeric HN protein, IM18, which induced fusion either with chimera no. 36 or with the SV41 F protein similarly to the SV41 HN protein. We thus conclude that the F protein specificity of the HN protein that is observed in the fusion event is not solely defined by the primary structure of the HN stalk domain. IMPORTANCE: It is appreciated that the HN head domain initially conceals the HN stalk domain but exposes it after the head domain has bound to the receptors, which allows particular @entity1522 in the stalk domain to interact with the F protein and trigger it to induce fusion. However, other regulatory roles of the HN head domain in the fusion event have been ill defined. We have shown in the current study that removal of the head domain or @entity3689 substitutions in a particular region of the head domain drastically change the F protein specificity of the HN protein, suggesting that the ability of a given HN protein to interact with an F protein is not only defined by the primary structure of the HN stalk domain but also by its conformation. This notion seems to account for the unidirectional substitutability among @entity68082 in triggering noncognate F proteins.

The fusion protein specificity of the XXXX virus hemagglutinin-neuraminidase protein is not solely defined by the primary structure of its stalk domain.

@entity1522 :: ('CHEBI:33709', 'Chemical') :: ['amino acids'] @entity38545 :: ('11212', 'Species') :: ['HPIV2', 'PIV5'] @entity15609 :: ('MESH:D018184', 'Disease') :: ['parainfluenza'] @entity68082 :: ('MESH:D019351', 'Disease') :: ['rubulavirus HN proteins'] @entity3689 :: ('D000596', 'Chemical') :: ['amino acid']
@entity15609 :: (MESH:D018184,Disease) :: ['parainfluenza']
