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Journal of Bacteriology, October 2000, p. 5823-5831, Vol. 182, No. 20
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

The N-Terminal Region of the Oenococcus oeni Bacteriophage fOg44 Lysin Behaves as a Bona Fide Signal Peptide in Escherichia coli and as a cis-Inhibitory Element, Preventing Lytic Activity on Oenococcal Cells

Carlos São-José,1 Ricardo Parreira,2 Graça Vieira,1 and Mário A. Santos1,*

Centro de Genética e Biologia Molecular e Departamento de Biologia Vegetal, Faculdade de Ciências da Universidade de Lisboa, 1700 Lisbon,1 and Unidade de Virologia, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa, 1349-008 Lisbon,2 Portugal

Received 17 November 1999/Accepted 27 July 2000

The function of the N-terminal region of the Oenococcus oeni phage fOg44 lysin (Lys44) as an export signal was investigated. We observed that when induced in Escherichia coli, Lys44 was cleaved between residues 27 and 28 in a SecA-dependent manner. Lys44 processing could be blocked by a specific signal peptidase inhibitor and was severely reduced by modification of the cleavage site. The lethal effect of Lys44 expression observed in E. coli was ascribed to the presence of its N-terminal 27-residue sequence, as its deletion resulted in the production of a nontoxic, albeit active, product. We have further established that lytic activity in oenococcal cells was dependent on Lys44 processing. An active protein with the molecular mass expected for the cleaved enzyme was detected in extracts from O. oeni-infected cells. The temporal pattern of its appearance suggests that synthesis and export of Lys44 in the infected host progress along with phage maturation. Overall, these results provide, for the first time, experimental evidence for the presence of a signal peptide in a bacteriophage lysin. Database searches and alignment of protein sequences support the prediction that other known O. oeni and Lactococcus lactis phages also encode secretory lysins. The evolutionary significance of a putative phage lysis mechanism relying on secretory lytic enzymes is tentatively discussed, on the basis of host cell wall structure and autolytic capacity.

* Corresponding author. Mailing address: Departamento de Biologia Vegetal, Faculdade de Ciências da Universidade de Lisboa, R. Ernesto de Vasconcelos, Edo C2, Campo Grande, 1700 Lisbon, Portugal. Phone: 351-21-7500000. Fax: 351-21-7500048. E-mail: mario.santos{at}excite.com.

Journal of Bacteriology, October 2000, p. 5823-5831, Vol. 182, No. 20
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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