This is the online Principles of Protein Structure course at Birkbeck College (Univ. of London) which covers protein structure and geometry at all levels at an introductory level. There is a specific page on symmetry
(The affiliated Birkbeck link to the previously mentioned page is here.)
If you could be more specific I could probably assist a bit more and with more focus. I would be remiss in not asking if you've taken a look at Introduction to Protein Structure by Branden & Tooze which is a nice intro to protein structure and function at an upper level undergrad/intro grad level.
There is a review paper which I have laying somewhere around on protein symmetry. The citation is (looked it up on PubMed)
D.S. Goodsell & A.J. Olson. (2000) "Structural Symmetry and Protein Function." Annual Reviews of Biophysics and Biomolecular Structure. 29:105-153.
If you're looking for something more crystallographic in nature, well, plenty of good crystallography links out there, not to mention books with an emphasis on protein crystallography (Rhodes, MacRee, MacPherson).
If you're looking for something more in the veins of good old fashioned inorganic chemistry/group theory related, probably will want to check out the Chemical Reviews issue dedicated to bioinorganic chemistry and dig about for mentions of symmetry in the articles (including the Holm/Solomon review on metals in biology in general).
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