The interesting case of the thermostable behaviour of α-carbonic anhydrase from lizard femoral gland secretions

Carbonic anhydrases (CAs) are essential metalloenzymes that catalyse the reversible hydration of carbon dioxide, playing a crucial role in various physiological processes. Given their potential for industrial use as biocatalysts for CO2 sequestration, there’s a growing interest in CAs from organisms adapted to extreme environments. This study focuses on a specific α-CA, CA-IV-like, recently identified in the femoral gland secretions of lizards. Under the “homeostatic function hypothesis,” this enzyme is posited to stabilize chemical communication signals left in the environment, suggesting it should be robust to thermal stress. To test this, we conducted a preliminary assessment of the effect of thermal treatment on the CA activity in femoral gland secretions from the lizard Podarcis muralis. Using protonography to measure enzyme activity and mass spectrometry to confirm the identity of the active protein, we incubated samples of the hydrophilic fraction of the secretion including CA at temperatures ranging from 20 °C to 100 °C. Our results show that the overall CA activity remains at approximately 50% even after a 15-minute incubation at 100 °C. This thermostability is significantly higher than that of known mammalian CAs, and comparable to those found in thermophilic bacteria. Further analysis revealed that CA-IV-like exists in the mixture in both monomeric and dimeric forms. While the dimeric form denatures and loses activity between 50 °C and 60 °C, the monomeric form maintains its activity. This remarkable stability suggests that lizard CA-IV-like is naturally adapted to the high-temperature conditions of its habitat. Our findings support the homeostatic function hypothesis and highlight this lizard enzyme as an interesting candidate for more in-depth investigations, primarily aimed at determining whether the observed thermostability is an intrinsic property or it is conferred by other factors occurring in the blend.