We report here on a combined photoemission and vibrational spectroscopy investigation of (S)-glutamic acid adsorption on Ag(111). We show that, in the temperature range 250 K <= T <= 400 K, non-zwitterionic adsorption takes place and the anionic form prevails at nonvanishing coverage. Significant conformational changes of the self-assembled layer must occur above 300 K, corresponding to a substantial reduction of the sticking probability and a modification of the vibrational spectrum. The similarity of behavior with respect to glutamic acid adsorption on the previously investigated Ag(100) and Ag(110) surfaces is also discussed.