Calcium complexation by steroids involved in the steroidogenesis

Area of Science:

• Biochemistry
• Analytical Chemistry
• Computational Chemistry

Background:

• Steroid hormones are vital in human physiology, participating in numerous biological processes.
• Steroidogenesis pathways involve interactions between steroids and calcium ions.
• Understanding these interactions is key to elucidating steroid hormone function.

Purpose of the Study:

• To determine the binding selectivities and affinities of various human steroid classes for calcium.
• To characterize the adduct profiles and relative stabilities of steroid-calcium complexes.
• To differentiate binding behaviors among steroid isomers using advanced analytical techniques.

Main Methods:

• Electrospray Ionization-Mass Spectrometry (ESI-MS) was employed to study steroid-calcium binding.
• High resolution and tandem mass spectrometry characterized steroid adduct profiles.
• Threshold collision-induced dissociation (E1/2) assessed adduct stability; Density Functional Theory (DFT) modeled complexes.

Main Results:

• Doubly-charged steroid-calcium complexes ([nM + Ca]2+) were predominant.
• Specific adducts ([5M + Ca]2+) characterized 3-keto-steroids; water adducts ([nM + Ca + mH2O]2+) were observed for hindered ketones.
• Principal Component Analysis revealed distinct binding differences among steroid isomers.

Conclusions:

• ESI-MS effectively differentiates calcium-binding characteristics of steroid classes and isomers.
• Computational modeling corroborated experimental findings on steroid-calcium complex stability and binding modes.
• The study provides novel insights into the gas-phase interactions between calcium and diverse human steroid hormones.