I don't think that D1 plays role in photoprotection because this proteins has high turnover and gets degraded at high light.

Good paper:

Proc. Natl . Acad. Sci . USA

Vol. 95, pp. 364 –369, Januar y 1998

Plant Biolog y

It actually functions to support a removal of electrones from PSII which is extremely valuable protective function under conditions of high excitation of PSII (provoked by intense light, UV). It's increased turnover under high UV indeed is also a part of the protective function as it partially assimilates an e-excitation energy.

cyanobacteria possess a family of psbA genes, expressing two to six D1 isoforms. Some D1 isoforms are more stable under certain conditions. There is an intricate transcriptional regulation of which psbA gene is expressed under which conditions e.g. under HL/LL, under UV, high/low O2 levels, etc. D1 proteins are indeed generally prone to degradation but are not directly involved in photoprotection. Other PSII (-associated) pigments and proteins play a role in that.

I agree with reply of Prof. Janssen.

D1 protein isoforms bind/carry the prostetic groups (http://www.ncbi.nlm.nih.gov/pubmed/23786371 + my first reference) in a particular proximity to each other in PSII. It allows the protecting detour of excitation from one prostetic group to another in a rate/ speed which depends on a D1 isoform. The energy dissipating in this process is buffered by D1 conformation change/protein degradation.

It is still a role in photoprotection. However, it is not my particular subject :)