Hemagglutinin-neuraminidase (HN) secondary binding site (HN Site II)

The Hemagglutinin-neuraminidase (HN) secondary binding site, frequently referred to as Site II, is a distinct pocket located at the dimer interface of the HN glycoprotein in several paramyxoviruses, most notably human parainfluenza virus type 3 (hPIV3) (Zhang et al., 2013). Unlike the primary catalytic site (Site I) which exhibits neuraminidase activity, Site II is specialized for stable attachment to α2,6-linked sialic acid residues on the host cell surface (Aoyama et al., 2009). This binding event is a critical trigger for the conformational changes in the HN tetramer that are necessary to activate the associated Fusion (F) protein, thereby facilitating viral entry into the respiratory epithelium (Porotto et al., 2012). As an essential component of the viral entry mechanism, Site II is a high-value therapeutic target for the development of entry inhibitors and antiviral agents. Small molecule inhibitors and sialic acid mimetics, such as BCX 2798, are designed to occupy this site to prevent the HN-F interaction and neutralize the virus (Villar & Hernandez, 2017). Targeting this specific interface offers a strategy to block infection at its earliest stage, although the potential for viral resistance through site mutations remains a significant therapeutic challenge.

Other names

HN dimer interface binding siteHN Site IISecondary receptor binding site of HNParainfluenza virus HN secondary siteα2,6-sialic acid binding site of HN

Competitive inhibition of sialic acid binding at the secondary site of the HN protein, preventing the conformational change required to trigger the fusion (F) protein.