title: Diverse C-Terminal Sequences Involved in Flavobacterium johnsoniae Protein Secretion.
abstract: Flavobacteriumjohnsoniaeand many related bacteria secrete proteins across the outer membrane using the type IX secretion system (T9SS). Proteins secreted by T9SSs have amino-terminal signal peptides for export across the cytoplasmic membrane by the Sec system and carboxy-terminal domains (CTDs) targeting them for secretion across the outer membrane by the T9SS. Most but not all T9SS CTDs belong to the family TIGR04183 (type A CTDs). We functionally characterized diverse CTDs for secretion by theF. johnsoniaeT9SS. Attachment of the CTDs fromF. johnsoniaeRemA, AmyB, and ChiA to the foreign superfolder green fluorescent protein (sfGFP) that had a signal peptide at the amino terminus resulted in secretion across the outer membrane. In each case, approximately 80 to 100 amino acids from the extreme carboxy termini were needed for efficient secretion. Several type A CTDs from distantly related members of the phylumBacteroidetesfunctioned inF. johnsoniae, supporting the secretion of sfGFP by theF. johnsoniaeT9SS.F. johnsoniaeSprB requires the T9SS for secretion but lacks a type A CTD. It has a conserved C-terminal domain belonging to the family TIGR04131, which we refer to as a type B CTD. The CTD of SprB was required for its secretion, but attachment of C-terminal regions of SprB of up to 1,182 amino acids to sfGFP failed to result in secretion. Additional features outside the C-terminal region of SprB may be required for its secretion.IMPORTANCEType IX protein secretion systems (T9SSs) are common in but limited to members of the phylumBacteroidetesMost proteins that are secreted by T9SSs have conserved carboxy-terminal domains that belong to the protein domain family TIGR04183 (type A CTDs) or TIGR04131 (type B CTDs). Here, we identify features of T9SS CTDs ofF. johnsoniaethat are required for protein secretion and demonstrate that type A CTDs from distantly related members of the phylum function with theF. johnsoniaeT9SS to secrete the foreign protein sfGFP. In contrast, type B CTDs failed to target sfGFP for secretion, suggesting a more complex association with the T9SS.
authors.affiliation: Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA.
authors.forename: Surashree S
authors.initials: SS
authors.lastname: Kulkarni
authors.affiliation: Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA.
authors.forename: Yongtao
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA.
authors.forename: Colton J
authors.initials: CJ
authors.lastname: Brendel
authors.affiliation: Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA mcbride@uwm.edu.
authors.forename: Mark J
authors.identifier: http://orcid.org/0000-0002-3798-6761
authors.initials: MJ
authors.lastname: McBride
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D058947:Bacterial Secretion Systems / Q000378:metabolism*; D005417:Flavobacterium / Q000378:metabolism*; D000072417:Protein Domains; D021382:Protein Sorting Signals; D021381:Protein Transport
chemical_list: D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; D021382:Protein Sorting Signals
keywords: Bacteroidetes; protein secretion