Stable Picodisc Assemblies from Saposin Proteins and Branched Detergents

Area of Science:

• Biochemistry
• Structural Biology
• Membrane Protein Research

Background:

• Studying membrane proteins requires maintaining their native structure after extraction from cell membranes.
• Current methods like detergents, nanodiscs, and peptidiscs have limitations, such as pH dependency.
• Picodiscs using saposin A are effective but typically stable only at acidic pH.

Purpose of the Study:

• To discover novel picodisc assemblies that are stable at neutral pH.
• To identify new saposin-detergent combinations for membrane protein solubilization.
• To expand the toolkit for studying membrane proteins.

Main Methods:

• Exploration of pairings between saposin proteins (SapA, SapB variant) and various detergents.
• Characterization of new picodisc assemblies using size-exclusion chromatography, native mass spectrometry, and small-angle X-ray scattering.
• Investigation of stability and assembly at neutral pH.

Main Results:

• Identified novel picodisc assemblies formed by saposin proteins and double-tail detergents at neutral pH.
• These new picodiscs demonstrate stability for weeks.
• Saposin A and an engineered saposin B variant (SapB^W) were shown to form stable picodisc assemblies.
• Double-tail detergents were key to forming these neutral pH-stable assemblies.

Conclusions:

• Developed new, stable picodisc systems for membrane protein research at neutral pH.
• These findings offer a broader range of tools for solubilizing and studying membrane proteins.
• The use of double-tail detergents represents a significant advancement in picodisc technology.