Thanks for the quick reply and pointing out t bunch of references.
Radiation damage has been pointed out as a cause for such feature. The following references were pointed out.Ravelli, R.B.G. & McSweeney, S.M. (2000). The 'fingerprint' that X-rays can leave on structures. Structure 8:315-328. Wiek et al. (2000) PNAS 97, 623-628, and Leiros et al. (2001) Acta Cryst. D 57, 488-497.
Subbu
