title: A novel N-terminal region of the membrane β-hexosyltransferase: its role in secretion of soluble protein by Pichia pastoris.
abstract: The β-hexosyltransferase (BHT) from Sporobolomyces singularis is a membrane-bound enzyme that catalyses transgalactosylation reactions to synthesize galacto-oligosaccharides (GOSs). To increase the secretion of the active soluble version of this protein, we examined the uncharacterized novel N-terminal region (amino acids 1-110), which included two predicted endogenous structural domains. The first domain (amino acids 1-22) may act as a classical leader while a non-classical signal was located within the remaining region (amino acids 23-110). A functional analysis of these domains was performed by evaluating the amounts of the rBHT forms secreted by recombinant P. pastoris strains carrying combinations of the predicted structural domains and the α mating factor (MFα) from Saccharomyces cerevisiae as positive control. Upon replacement of the leader domain (amino acids 1-22) by MFα (MFα-rBht(23-594)), protein secretion increased and activity of both soluble and membrane-bound enzymes was improved 53- and 14-fold, respectively. Leader interference was demonstrated when MFα preceded the putative classical rBHT(1-22) leader (amino acids 1-22), explaining the limited secretion of soluble protein by P. pastoris (GS115 : : MFα-rBht(1-594)). To validate the role of the N-terminal domains in promoting protein secretion, we tested the domains using a non-secreted protein, the anti-β-galactosidase single-chain variable antibody fragment scFv13R4. The recombinants carrying chimeras of the N-terminal 1-110 regions of rBHT preceding scFv13R4 correlated with the secretion strength of soluble protein observed with the rBHT recombinants. Finally, soluble bioactive HIS-tagged and non-tagged rBHT (purified to homogeneity) obtained from the most efficient recombinants (GS115 : : MFα-rBht(23-594)-HIS and GS115 : : MFα-rBht(23-594)) showed comparable activity rates of GOS generation.
authors.affiliation: Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC 27695-7615, USA.
authors.forename: Suzanne F
authors.initials: SF
authors.lastname: Dagher
authors.affiliation: Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC 27695-7615, USA.
authors.forename: José M
authors.initials: JM
authors.lastname: Bruno-Bárcena
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D006602:Hexosyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D010843:Pichia / Q000235:genetics* / Q000378:metabolism; D021381:Protein Transport; D015003:Yeasts / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics
chemical_list: D005656:Fungal Proteins; D006602:Hexosyltransferases