MA silk properties have traditionally been thought to be the product of the combined expression of genes coding for two proteins (called spidroins); major ampullate spidroin 1, or MaSp1, and major ampullate spidroin 2, or MaSp2  (with the genes called MaSp1 and MaSp2). The secondary structures of the spidroins are considered critical for silk performance . MaSp1 consists of repeating polyalanine, (GA)n, (GGX)n and (A)n amino acid motifs (G = glycine, A = alanine and X = other amino acids). These motifs form cassettes that combine to promote the formation of crystalline β–sheet nanostructures in the assembled fibers . The MaSp2 protein on the other hand has been thought to consist of multiple (GPGXX)n motifs (where P = proline), and predicted to form disordered type II β-turns and similar non-crystalline nanostructures . Collectively, the various nanostructures are thought to combine and provide MA silk with its great strength and extensibility . Since MaSp2 has long been predicted to contain (GPGXX)n sequences, the proline composition of MA silk was considered a reliable indicator of MaSp2 gene expression . The ratio of MaSp1: MaSp2 expression is variable among and between spider species, presumably because the MaSp2 protein is metabolically costly to synthesize so may be differentially expressed. Variation in the ratio of the two spidroins has been traditionally thought to bring about variations in nanostructure formations leading to variations in the mechanics of the spun fibres .