Identification and Characterization of Novel Chitin-Binding Proteins from the Larval Cuticle of Silkworm, Bombyx mori

Cuticle is mainly made of chitin
filaments embedded in a matrix
of cuticular proteins (CPs). Cuticular chitins have minor differences,
whereas CPs are widely variable with respect to their sequences and
structures. To understand the molecular basis underlying the mechanical
properties of cuticle, it is necessary to know which CPs interact
with chitin and how they are assembled into the cuticle structure.
In the present study, a chitin-binding assay was performed followed
by liquid chromatography–tandem mass spectrometry to identify
the extracted proteins from the larval cuticle of silkworm, Bombyx mori. There were 463 proteins identified from
the silkworm larval cuticle, 200 of which were recovered in the chitin-binding
fraction. A total of 103 proteins were annotated as CPs, which were
classified into 11 CP families based on their conserved motifs, including
CPR, CPAP, CPT, CPF and CPFL, CPCFC, chitin_bind 3, BmCPH2 homologues,
BmCPH9 homologues, BmCPG1 homologues, BmCPG20 homologues, and BmCPG21
homologues. A total of five CP families were newly identified in the
chitin-binding fraction, thereby providing new information and insight
into the composition, structure, and function of the silkworm larval
cuticle.