Spider Egg Case Core Fibers: Trimeric Complexes Assembled from TuSp1, ECP-1, and ECP-2 †

Spider silk proteins are well-known for their extraordinary mechanical properties, displaying remarkable strength and toughness. In this study, matrix-assisted laser desorption ionization (MALDI) tandem time-of-flight (TOF) mass spectrometry (MS/MS) and reverse genetics were used to isolate a new cDNA sequence that encodes for a protein assembled into egg case silk from the black widow spider, Latrodectus hesperus. Analysis of the primary sequence of this protein reveals ∼52% identity to the egg case protein 1 (ECP-1) fibroin-like family member. On the basis of the similarity in the primary sequence and expression pattern, we have named this factor egg case protein 2 (ECP-2). Alignments of ECP-1 and ECP-2 demonstrate highly conserved N termini, with 16 Cys residues found within the first 153 amino acids. Traditional ensemble repeats found within reported fibroins were poorly represented in the primary sequence of ECP-2, but scattered blocks of polyalanine were present, along with a C terminus rich in GA r...