Coordination to lanthanide ions distorts binding site conformation in calmodulin

Abstract

The Ca-sensing protein calmodulin (CaM) is a popular model of biological ion binding since it is both experimentally tractable and essential to survival in all eukaryotic cells. CaM modulates hundreds of target proteins and is sensitive to complex patterns of Ca exposure, indicating that it functions as a sophisticated dynamic transducer rather than a simple on/off switch. Many details of this transduction function are not well understood. Fourier transform infrared (FTIR) spectroscopy, ultrafast 2D infrared (2D IR) spectroscopy, and electronic structure calculations were used to probe interactions between bound metal ions (Ca and several trivalent lanthanide ions) and the carboxylate groups in CaM's EF-hand ion-coordinating sites. Since Tb is commonly used as a luminescent Ca analog in studies of protein-ion binding, it is important to characterize distinctions between the coordination of Ca and the lanthanides in CaM. Although functional assays indicate that Tb fully activates many Ca-dependent proteins, our FTIR spectra indicate that Tb, La, and Lu disrupt the bidentate coordination geometry characteristic of the CaM binding sites' strongly conserved position 12 glutamate residue. The 2D IR spectra indicate that, relative to the Ca-bound form, lanthanide-bound CaM exhibits greater conformational flexibility and larger structural fluctuations within its binding sites. Time-dependent 2D IR lineshapes indicate that binding sites in Ca-CaM occupy well-defined configurations, whereas binding sites in lanthanide-bound-CaM are more disordered. Overall, the results show that binding to lanthanide ions significantly alters the conformation and dynamics of CaM's binding sites.

Lanthanides compete with calcium for binding to cadherins and inhibit cadherin-mediated cell adhesion

“…Interestingly, a recent study found that binding of Tb 3+ to another Ca 2+ -dependent protein, calmodulin, resulted in enhanced structural flexibility within Ca 2+ -binding sites and this was caused by the more electropositive Tb 3+ adopting an alternative and more disordered coordination geometry. 49 In the case of cadherins, changes in coordination geometry and flexibility within binding sites may also be the chemical driving forces behind global differences in Tb 3+ -bound and Ca 2+ -bound molecules. However, unlike in calmodulin, cadherins are non-functional upon binding to Tb 3+ , which provides further insight into the high level of sensitivity of cadherins to Ca 2+ chemistry.…”

The Chemistry of Lanthanides in Biology: Recent Discoveries, Emerging Principles, and Technological Applications

“…Studies have suggested positive impacts of RE provision in animal husbandry, suggesting a role for REs in higher organisms. 128 However, REs are not perfect mimics of Ca, 4 as recent studies of calmodulin 129,130 and cadherin 131 have shown, suggesting that REs may not play a general role as Ca substitutes in Ca-dependent proteins. Instead, the growth-promoting effects of REs in higher organisms might plausibly be linked to the microbiome; for example, both beneficial ( E. coli ) and pathogenic ( Pseudomonas aeruginosa ) bacteria possess PQQ-dependent dehydrogenases, and these or other enzymes might benefit from or be inhibited by REs.…”

Amyloid found in human cataracts with two-dimensional infrared spectroscopy

“…Coherent vibrations provide structural information by changing the absorption frequencies, anharmonicity, and vibrational dynamics (26,27). Two-dimensional infrared (2DIR) spectroscopy uses a series of femtosecond mid-IR pulses to measure these properties by correlating vibrational modes, similar to how 2D NMR correlates nuclear spins (28). A pair of pump pulses excites the vibrational modes (ω pump axis), while a probe pulse measures how that mode and all of the other modes in the system respond (ω probe axis).…”