L-29, a soluble lactose-binding lectin, is phosphorylated on serine 6 and serine 12 in vivo and by casein kinase I.
L-29, a mammalian soluble lactose-binding lectin, was previously shown to be phosphorylated in confluent 3T3 fibroblasts (Cowles, E. A., Agrwal, N., Anderson, R. L., and Wang, J. L. (1990) J. Biol. Chem. 265, 17706-17712), which contain a small amount of this protein. We have determined the site of phosphorylation on L-29, taking advantage of the abundance of L-29 (about 1% of total soluble cell protein) in confluent polarized Madin-Darby canine kidney (MDCK) cells. Approximately 15-20% of the L-29 is phosphorylated in these cells. Phosphoamino acid analysis showed phosphate incorporation only at serine. Analysis of chymotryptic and endoproteinase Asp-N-generated NH2-terminal fragments by Edman degradation showed that 90% of the phosphate was at Ser6 and 10% at Ser12. The sequence surrounding Ser6, which is conserved in all known L-29 sequences, indicated that this serine might be phosphorylated by casein kinase I or casein kinase II. Reaction of human recombinant L-29 with [gamma-32P]ATP and each of these casein kinases showed that only casein kinase I catalyzed significant incorporation of 32P into L-29; and, as with the L-29 from the MDCK cell extracts, most of the phosphate was incorporated at Ser6 and a small amount was incorporated at Ser12.
Huflejt
M E
ME
Department of Psychiatry, University of California, San Francisco 94143.
Turck
C W
CW
Lindstedt
R
R
Barondes
S H
SH
Leffler
H
H
D000595:Amino Acid Sequence; D000818:Animals; D000943:Antigens, Differentiation / Q000378:metabolism*; D047388:Casein Kinases; D002460:Cell Line; D004285:Dogs; D037502:Galectin 3; D006825:Hybridomas; D037102:Lectins / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D012694:Serine / Q000378:metabolism*
D000943:Antigens, Differentiation; D037502:Galectin 3; D037102:Lectins; D012694:Serine; D011494:Protein Kinases; D047388:Casein Kinases