Structural insights into human signal peptide peptidase

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Signal peptide peptidase (SPP) is the sole intramembrane protease family lacking structural characterization.
• Understanding SPP structure is crucial for elucidating intramembrane protease mechanisms.

Purpose of the Study:

• To determine the cryo-electron microscopy (cryo-EM) structures of human SPPL2a.
• To characterize SPPL2a in both ligand-free and inhibitor-bound states.
• To gain insights into substrate gating and inhibitor recognition in aspartyl intramembrane proteases.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine high-resolution structures.
• Analysis of SPPL2a in ligand-free and inhibitor-bound (L685,458) states.
• Comparative structural analysis with presenilin 1 (PS1).

Main Results:

• Obtained cryo-EM structures of human SPPL2a at 3.3 and 3.6 Å resolution.
• Identified a conserved fold among SPP and presenilin families, with nine transmembrane helices.
• Observed distinct conformational states, including a pre-formed β-hairpin and inhibitor-induced rearrangements.

Conclusions:

• The structures provide the first high-resolution insights into the SPP family.
• Findings illuminate mechanisms of selective inhibitor recognition and substrate gating.
• Structure-based analysis reveals key differences between SPP and presenilin families impacting function and assembly.