infrared and Raman spectroscopy were applied to identify restraints for the structure determination of the 20 amino acid loop between two P-sheets of the N-terminal region of the PsbQ protein of the oxygen evolving complex of photosystem 11 from Spinacia oleracea by restraint-based homology modeling. One of the initial models has shown a stable fold of the loop in a 20 ns molecular dynamics simulation that is in accordance with spectroscopic data. Cleavage of the first 12 amino acids leads to a permanent drift in the root means square deviation of the protein backbone and induces major structural changes. (c) 2006 Elsevier Inc. All rights reserved.