Structural features of glycosyltransferases synthesizing major bilayer and nonbilayer-prone membrane lipids in Acholeplasma laidlawii and Streptococcus pneumoniae.
In membranes of Acholeplasma laidlawii two consecutively acting glucosyltransferases, the (i) alpha-monoglucosyldiacylglycerol (MGlcDAG) synthase (alMGS) (EC ) and the (ii) alpha-diglucosyl-DAG (DGlcDAG) synthase (alDGS) (EC ), are involved in maintaining (i) a certain anionic lipid surface charge density and (ii) constant nonbilayer/bilayer conditions (curvature packing stress), respectively. Cloning of the alDGS gene revealed related uncharacterized sequence analogs especially in several Gram-positive pathogens, thermophiles and archaea, where the encoded enzyme function of a potential Streptococcus pneumoniae DGS gene (cpoA) was verified. A strong stimulation of alDGS by phosphatidylglycerol (PG), cardiolipin, or nonbilayer-prone 1,3-DAG was observed, while only PG stimulated CpoA. Several secondary structure prediction and fold recognition methods were used together with SWISS-MODEL to build three-dimensional model structures for three MGS and two DGS lipid glycosyltransferases. Two Escherichia coli proteins with known structures were identified as the best templates, the membrane surface-associated two-domain glycosyltransferase MurG and the soluble GlcNAc epimerase. Differences in electrostatic surface potential between the different models and their individual domains suggest that electrostatic interactions play a role for the association to membranes. Further support for this was obtained when hybrids of the N- and C-domain, and full size alMGS with green fluorescent protein were localized to different regions of the E. coli inner membrane and cytoplasm in vivo. In conclusion, it is proposed that the varying abilities to bind, and sense lipid charge and curvature stress, are governed by typical differences in charge (pI values), amphiphilicity, and hydrophobicity for the N- and (catalytic) C-domains of these structurally similar membrane-associated enzymes.
Edman
Maria
M
Department of Biochemistry, Umeå University, Sweden.
Berg
Stefan
S
Storm
Patrik
P
Wikström
Malin
M
Vikström
Susanne
S
Ohman
Anders
A
Wieslander
Ake
A
D000128:Acholeplasma laidlawii / Q000378:metabolism*; D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D016695:Glycosyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008051:Lipid Bilayers; D008563:Membrane Lipids / Q000096:biosynthesis*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D013296:Streptococcus pneumoniae / Q000378:metabolism*
D017931:DNA Primers; D008051:Lipid Bilayers; D008563:Membrane Lipids; D016695:Glycosyltransferases