Apo-metallothionein-3 cooperatively forms tightly compact structures under physiological conditions.

Area of Science:

• Biochemistry
• Structural Biology
• Neuroscience

Background:

• Metallothioneins (MTs) are crucial metal-binding proteins in mammals.
• MT isoform 1 (MT1) is found in kidneys, while MT isoform 3 (MT3) is in nervous tissue.
• The structures of metal-bound MT1/MT2 are known, but apo-MT3 structure remains largely uncharacterized.

Purpose of the Study:

• To elucidate the structure and dynamics of apo-MT3 under physiological and denaturing conditions.
• To compare the structural properties and cysteine accessibility of apo-MT3 with apo-MT1.
• To provide insights into the distinct roles of MT3 in the nervous system versus MT1 in the kidneys.

Main Methods:

• Cysteine modification coupled with electrospray ionization mass spectrometry (ESI-MS).
• Denaturing reactions with guanidinium chloride and stopped-flow kinetics.
• Ion mobility mass spectrometry (IM-MS) and molecular dynamics (MD) simulations.

Main Results:

• Apo-MT3 adopts a compact structure under physiological conditions and an extended structure under denaturing conditions.
• Apo-MT3 exhibits more cooperative binding to cysteine modifiers and slower modification rates compared to apo-MT1.
• IM-MS can distinguish apo-MT3 as a distinct structural population.

Conclusions:

• Apo-MT3 possesses a unique compact structure influencing its cysteine accessibility.
• These findings support MT3's role as a noninducible regulator in the nervous system.
• MT1 functions as an inducible scavenger of metals in the kidneys, contrasting with MT3's role.