A putative lipoprotein of Sphingomonas sp. strain A1 binds alginate rather than a lipid moiety

Gram-negative Sphingomonas sp. strain A1 accumulates alginate in the cell surface pit and directly incorporates the polysaccharide into its cytoplasm through a 'superchannel'. A cell surface protein Algp7 (27 kDa) is inducibly expressed in the presence of alginate. Although the protein Algp7 was initially classified as a lipoprotein based on its primary structure, Algp7 purified from strain A1 cells did not possess a lipid moiety. Algp7 bound alginate efficiently at a neutral pH with a K(d) of 3.6 x 10(-8) M, suggesting that the cell surface protein contributed to accumulation of alginate in the pit.