The C-terminal half of Dpfp1 is dominated by the previously reported 13 amino acid consensus sequence: K-P-G-P-Y-D-Y-D-G-P-Y-D-K (Rzepecki and Waite, 1993).
MALDI-TOF analysis of native Dpfp1 indicates that the purified protein is represented by two major mass variants.
First, the size of the composite sequence (1481 bases) closely matches the size of the largest Dpfp1 transcript as determined by Northern blots of zebra mussel foot tissue mRNA hybridized to a Dpfp1-specific probe.
Table I Amino acid composition of deduced and native Dpfp1 Amino acid Native Deduced Asx 136.
In previous studies, isoelectric focusing of purified Dpfp1 suggested the presence of at least 10 electrophoretic variants in the polymorphic family (Rzepecki and Waite, 1993).
This is especially true of proline, tyrosine, aspartic acid, lysine, threonine, and glycine residues, which together account for almost 75% of the amino acid composition of Dpfp1.
More than 80% of the deduced primary amino acid sequence of Dpfp1 is composed of tandemly repeated and segregated motifs: one is a heptapeptide; the other, a tridecapeptide consensus motif that coincides with peptides sequenced previously (Rzepecki and Waite, 1993).
The N-terminal half of Dpfp1 is dominated by a heptapeptide motif that is repeated 22 times with some variation, particularly at position #7 of the consensus sequence.
The N-terminal half of Dpfp1 differs significantly from the C-terminal domain with its repeated 13 amino acid motif [ILLUSTRATION FOR FIGURE 4 OMITTED].