Methylamines keep hagfish slime thread skeins together

Abstract

Hagfish have a rather gruesome reputation. Gorging on victims from the inside out, hagfish are also infamous for disabling adversaries with a viscous slime that clogs gills, asphyxiating them. ‘Slime exudate released by a hagfish reacts with water to form slime in less than 400 ms; only 50 mg of dried mucus and threads are needed to make approximately 1 litre of slime’, marvels Gaurav Jain from Chapman University, USA. Prior to release, the reinforcing threads that strengthen the slime are stored in tightly balled skeins secured with adhesive, which unravel rapidly as the adhesive is washed away by seawater. However, Doug Fudge, also from Chapman University, and Jain had noticed that the stabilising solution within the slime glands in which the skeins are stored contains unexpectedly high levels of a group of compounds known as methylamines. ‘They occur in the tissues of many marine organisms’, says Jain, explaining that the materials help to stabilize protein structures in the bodies of deep-sea dwellers. Could they also contribute to keeping hagfish slime filaments in check prior to deployment?Jain applied gentle electrical currents to the slime glands of anaesthetised Pacific and Atlantic hagfish to collect minute quantities of the concentrated milky slime. Then, Paul Yancey, from Whitman College, USA, analysed the components and found betaine and TMAO – two methylamine compounds – in the highest concentrations (over 200 mmol l−1 for betaine and 79–110 mmol l−1 for TMAO), with traces of amino acids and sugars making up the other components. But what effects did the various compounds have on the stability of the tightly coiled skeins?This time, Jain and undergraduates Marie Starksen, Kashika Singh and Chris Hoang mixed tiny droplets of the concentrated slime with a solution containing increasing doses (from 100 mmol l−1 up to 1 mol l−1) of the individual constituents – including the methylamines TMAO, betaine and dimethylglycine, and the amino acid glycine – and watched the effects on the skeins of thread before Charlene McCord plotted the degree of unravelling against the concentration of each solution. Would the skeins unravel or remain tightly coiled?At lower concentrations, none of the constituent compounds had any stabilising effect, with the thread skeins falling apart rapidly after the droplet was applied. However, as the concentration of TMAO increased to 400 mmol l−1, the skeins began holding together and by the time Jain increased the concentrations of betaine and dimethylglycine to their highest levels (1 mol l−1), those skeins also remained largely intact. ‘We were surprised that TMAO was much more effective at preventing skein unravelling than any other methylamines, even though it was present in much lower amounts in the hagfish slime’, says Jain. And when he combined one part TMAO with two parts betaine before adding them to the unexploded slime threads, he was impressed to see that the combination had an even more powerful stabilising effect than the individual components, keeping the skeins tightly wound.It seems that the methylamines TMAO and betaine are essential for keeping the skeins tightly packaged while in storage. However, the stabilising compounds wash away rapidly when hagfish squirt their concentrated pre-slime into seawater, ready to engulf any threat or meal that comes their way.