expression, godan verb (-ru)
serve loyally; wait on hand and foot; be at someone's beck and call
Idiomatic expression meaning to act as someone's devoted helper, doing whatever they need. The reading しゅそくとなる is rare and literary.
彼は社長の手足となって働いている。
He works as the president's right-hand man.
The secretary acts at the boss's beck and call.