Using the full-length amino-acid sequences of the human beta1,3
galactosyltransferase (beta3GalT)-I, -II and III
enzymes as query, we have identified an additional member of the beta3GalT gene family within a sequenced region of the human chromosome 21 as found in GenBank. The novel human
beta3GalT-V gene included an open reading frame of 933 bp encoding a
protein of 310
amino acids with a short N-terminal cytoplasmic tail, a single predicted transmembrane domain and a large lumenal catalytic domain. The human
beta3GalT-V protein showed 34%, 27%, 31% and 23% sequence identity with the human beta3GalT-I, -II, -III and -IV
enzymes, respectively. The expression of
beta3GalT-V as a
recombinant protein in Sf9 insect cells confirmed the
galactosyltransferase activity catalyzed by this
enzyme. Similarly to beta3GalT-I, -II and -III, the
beta3GalT-V enzyme used beta-linked GlcNAc as an acceptor, but unlike the former
enzymes beta3GalT-V exhibited a marked preference for the O-linked core3 GlcNAcbeta1,3GalNAc substrate. The
beta3GalT-V gene was mainly expressed in human small intestine and to a lesser extent in pancreas and testis. Although
beta3GalT-V transcripts were not detected in normal colon tissue, based on Northern analysis,
beta3GalT-V mRNA was found in the
adenocarcinoma cell line Colo 205.