A true autoactivating enzyme. Structural insight into mannose-binding lectin-associated serine protease-2 activations

Area of Science:

• Biochemistry
• Structural Biology
• Immunology

Background:

• The lectin pathway is crucial for innate immunity, initiating complement activation.
• Mannose-binding lectin-associated serine protease-2 (MASP-2) is the initiating enzyme in this pathway.
• Understanding MASP-2 autoactivation is key to its function in complement.

Purpose of the Study:

• To elucidate the structural and mechanistic basis of MASP-2 autoactivation.
• To characterize the autoactivation process of a MASP-2 catalytic fragment.
• To provide insight into the transition from zymogen to active MASP-2.

Main Methods:

• Crystallography was used to determine the structure of proenzyme MASP-2 catalytic fragment at 2.4 A resolution.
• Comparative structural analysis of zymogen and active MASP-2 forms.
• Biochemical assays to assess substrate cleavage by zymogen MASP-2.

Main Results:

• Zymogen MASP-2 exhibits intrinsic catalytic activity against its natural substrate C4, albeit at reduced efficiency (10% of active MASP-2).
• Significant conformational changes occur in the serine protease domain beyond the activation domain in zymogen MASP-2.
• These conformational dynamics are proposed to facilitate the transition to the active state.

Conclusions:

• MASP-2 autoactivation is an intrinsic process involving conformational flexibility.
• The study provides a structural model for the active zymogen MASP-2 complex.
• A mechanism for MASP-2 autoactivation is proposed based on structural and functional data.