Regulation of insect flight muscle
Insect flight muscles can contract at high frequency because they are part of a resonant system consisting of the muscles, thorax and wings. In asynchronous flight muscle, contractions are triggered by periodic stretches which activate the muscle after a delay. These muscles are only partially activated by calcium released as a result of nerve stimulation and must be stretched by 1 to 3% for full tension development. We are investigating two aspects of stretch-activation: 1) Large modular proteins that are probably responsible for the high stiffness of flight muscle and 2) regulatory proteins on the thin filaments that may be affected by stretching the muscle.
1. Large modular proteins
Insect muscles have a modular protein of 800 kDa (projectin) associated
with the thick filaments. In the flight muscle, projectin links
thick filaments to the Z-disc and may transmit tension to the
filaments when the muscle fibres are stretched, as well as contributing
to the stiffness of the fibres. Projectin consists of immunoglobulin
(Ig) and fibronectin (Fn)-like domains, similar to vertebrate
muscle titin. We are determining the orientation of the molecule
in the muscle sarcomere by immuno-electron microscopy.
Kettin is another modular protein (500-700 kDa) which is in the
Z-disc and extends from it about 100 nm. Kettin is associated
with actin filaments and may reinforce the Z-disc structure by
crosslinking actin filaments. We have determined the position
and orientation of the molecule by immuno-electron microscopy
and are investigating the affinity of the binding to actin and
the position of the binding site. One module of kettin binds to
one actin subunit in the filament.
Work on modular proteins is with Monique van Straaten and David
Goulding.
2. Regulatory proteins on the thin filament
See the entry by Dr J.Clayton.
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(This was one of the first web pages at EMBL, set up by Jon Clayton in 1994).