  The iron stress-induced protein A (IsiA) is a source of interest and debate
in biological research. The IsiA super-complex, binding over 200 chlorophylls,
assembles in multimeric rings around photosystem I (PSI). Recently, the
IsiA-PSI structure was resolved to 3.48 {\AA}. Based on this structure, we
created a model simulating a single excitation event in an IsiA monomer. This
model enabled us to calculate the fluorescence and the localisation of the
excitation in the IsiA structure. To further examine this system, noise was
introduced to the model in two forms -- thermal and positional. Introducing
noise highlights the functional differences in the system between cryogenic
temperatures and biologically relevant temperatures. Our results show that the
energetics of the IsiA pigment-protein complex are very robust at room
temperature. Nevertheless, shifts in the position of specific chlorophylls lead
to large changes in their optical and fluorescence properties. Based on these
results we discuss the implication of highly robust structures, with potential
for serving different roles in a context dependent manner, on our understanding
of the function and evolution of photosynthetic processes.
