Check out the movies of the transition (in supplement). Might be interesting for morph server.
Nature 440, 372-376 (16 March 2006)
Structural basis for the spectral difference in luciferase bioluminescence
Toru Nakatsu, Susumu Ichiyama, Jun Hiratake, Adrian Saldanha, Nobuyuki Kobashi, Kanzo Sakata and Hiroaki Kato