LoopTK is a C++ toolkit for representing, modeling and manipulating proteins, protein fragments, and protein loops.
It has been designed to be easy to use and powerful at the same time.

LoopTK is developed and maintained by the Artificial Intelligence Laboratory at Stanford University.

Here are a few screenshots of the toolkit in action:

2CRO 1K96 1K96
Cutaway of the occupancy grid of 2CRO. Conformations of 1K96 generated using LoopTK. Image rendered in PyMOL. Animation of loop manipulation; each frame is generated and rendered in LoopTK.

Read about protein loop kinematics here.