Structural Basis of Sarco/Endoplasmic Reticulum Ca²⁺-ATPase 2b Regulation via Transmembrane Helix Interplay

Area of Science:

• Structural biology
• Membrane protein biochemistry
• Calcium signaling

Background:

• Sarco/endoplasmic reticulum Ca2+-ATPase 2b (SERCA2b) is crucial for calcium (Ca2+) transport.
• The regulatory role of SERCA2b's C-terminal segments, including the 11th transmembrane helix (TM11), is not fully understood.
• Understanding SERCA2b structure-function relationships is vital for cellular Ca2+ homeostasis.

Purpose of the Study:

• To elucidate the structural basis of SERCA2b regulation by its C-terminal segments, particularly TM11.
• To compare the crystal structures of SERCA2b and its splice variant SERCA2a.
• To investigate the functional impact of TM11 interactions on SERCA2b ATPase activity.

Main Methods:

• Determination of crystal structures for SERCA2b and SERCA2a in the E1-2Ca2+-AMPPCP state.
• Structural analysis of TM11 positioning and interactions with adjacent regions.
• Site-directed mutagenesis to disrupt TM11-neighboring residue interactions.

Main Results:

• Crystal structures revealed TM11 adjacent to TM10, interacting weakly with the L8/9 loop and TM10 N-terminus.
• These interactions were found to inhibit the SERCA2b catalytic cycle.
• Mutational disruption of TM11 interactions resulted in SERCA2b exhibiting SERCA2a-like ATPase activity.

Conclusions:

• TM11 acts as a key intrinsic modulator of SERCA2b activity.
• TM11 fine-tunes intramolecular interactions within the transmembrane domain to regulate the catalytic cycle.
• The findings provide structural insights into SERCA2b regulation and potential therapeutic targets.