Environmental conditions impinge on dragline silk protein composition

Abstract

The silk formed in the major ampullate (MA) gland of the orb weaving spider Nephila clavipes is composed of two silk fibroins, which are called major ampullate spidroins 1 (MaSp1) and 2 (MaSp2). Analysis of proteolytic peptides and reactivity to spidroin type specific antibodies indicated that MaSp2 constituted only a minor part in the spinning dope as well as in the spun filaments. Upon starvation, a change in the silk's characteristic features was observed that was concomitant of a decrease in the contribution of MaSp2. The silk became less elastic and stiffer, which will better tailor its usability for the safety line, albeit at the expense of its employment as the web frame threads. In addition, since MaSp2 production requires greater ATP consumption, such a shift in the protein ratio cuts down on the energy costs to produce the silk. From this change in protein composition the spider might therefore benefit twice, by synthesizing 'cheaper' silk that into the bargain has properties that potentially can better support foraging in times of food shortage.