Proteomic Evidence for Components of Spider Silk Synthesis from Black Widow Silk Glands and Fibers

Spider
silk research has largely focused on spidroins, proteins
that are the primary components of spider silk fibers. Although a
number of spidroins have been characterized, other types of proteins
associated with silk synthesis are virtually unknown. Previous analyses
of tissue-specific RNA-seq libraries identified 647 predicted genes
that were differentially expressed in silk glands of the Western black
widow, Latrodectus hesperus. Only ∼5%
of these silk-gland specific transcripts (SSTs) encode spidroins;
although the remaining predicted genes presumably encode other proteins
associated with silk production, this is mostly unverified. Here,
we used proteomic analysis of multiple silk glands and dragline silk
fiber to investigate the translation of the differentially expressed
genes. We find 48 proteins encoded by the differentially expressed
transcripts in L. hesperus major ampullate,
minor ampullate, and tubuliform silk glands and detect 17 SST encoded
proteins in major ampullate silk fibers. The observed proteins include
known silk-related proteins, but most are uncharacterized, with no
annotation. These unannotated proteins likely include novel silk-associated
proteins. Major and minor ampullate glands have the highest overlap
of identified proteins, consistent with their shared, distinctive
ampullate shape and the overlapping functions of major and minor ampullate
silks. Our study substantiates and prioritizes predictions from differential
expression analysis of spider silk gland transcriptomes.