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Journal of Virology, May 2002, p. 4603-4611, Vol. 76, No. 9
0022-538X/02/$04.00+0     DOI: 10.1128/JVI.76.9.4603-4611.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Fatty Acids on the A/USSR/77 Influenza Virus Hemagglutinin Facilitate the Transition from Hemifusion to Fusion Pore Formation

Tatsuya Sakai, Reiko Ohuchi, and Masanobu Ohuchi*

Department of Microbiology, Kawasaki Medical School, Kurashiki, Okayama 701-0192, Japan

Received 15 October 2001/ Accepted 17 January 2002

Influenza virus hemagglutinin (HA) has three highly conserved acylation sites close to the carboxyl terminus of the HA2 subunit, one in the transmembrane domain and two in the cytoplasmic domain. Each site is modified by palmitic acid through a thioester linkage to cysteine. To elucidate the biological significance of HA acylation, the acylation sites of HA of influenza virus strain A/USSR/77 (H1N1) were changed by site-directed mutagenesis, and the membrane fusion activity of mutant HAs lacking the acylation site(s) was examined quantitatively using transfer assays of lipid (R18) and aqueous (calcein) dyes. Lipid mixing, so-called hemifusion, activity was not affected by deacylation, whereas transfer of aqueous dye, so-called fusion pore formation, was dramatically restricted. When the fusion reaction was induced by a lower pH than the optimal one, calcein transfer with the mutant HAs was improved, but simultaneously a considerable calcein leakage into the medium was observed. From these results, we conclude that the palmitic acids on the H1 subtype HA facilitate the transition from hemifusion to fusion pore formation.

* Corresponding author. Mailing address: Department of Microbiology, Kawasaki Medical School, Kurashiki, Okayama 701-0192, Japan. Phone: 81-86-462-1111. Fax: 81-86-462-1199. E-mail: mohuchi{at}med.kawasaki-m.ac.jp.

Journal of Virology, May 2002, p. 4603-4611, Vol. 76, No. 9
0022-538X/02/$04.00+0     DOI: 10.1128/JVI.76.9.4603-4611.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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Copyright © 2002 by the American Society for Microbiology. All rights reserved.