Structural locations and functional roles of new subsites S5, S6, and S7 in memapsin 2 (beta-secretase)

Area of Science:

• Biochemistry
• Molecular Biology
• Neuroscience

Background:

• Memapsin 2 (beta-secretase) cleaves beta-amyloid precursor protein (APP), producing amyloid-beta (Abeta), a key factor in Alzheimer's disease pathogenesis.
• The active site of memapsin 2 binds eight substrate residues (P4-P4'), influencing its enzymatic activity.

Purpose of the Study:

• To investigate the influence of additional substrate residues (P5-P7) on memapsin 2's hydrolytic activity.
• To characterize the substrate preferences of these extended subsites and their binding interactions.

Main Methods:

• Crystallography was used to determine the structure of memapsin 2 complexed with inhibitors, revealing binding interactions.
• Kinetic studies (K(m), k(cat)) were performed to quantify the impact of extended substrate residues on enzyme activity.
• Analysis of inhibitor OM03-4 bound to memapsin 2 elucidated specific subsite interactions.

Main Results:

• The addition of substrate residues P5-P7 significantly influences memapsin 2 activity, with a preference for hydrophobic residues, especially tryptophan.
• Crystal structures revealed the binding of P5-P7 residues and identified tryptophan interaction with the S6 subsite.
• Kinetic data showed decreased K(m) and increased k(cat) values with extended substrate residues, indicating improved substrate recognition and transition-state binding.

Conclusions:

• Substrate residues P5-P7 play a critical role in both memapsin 2 substrate recognition and transition-state binding.
• The S6 subsite's preference for hydrophobic residues, particularly tryptophan, is a key feature for efficient memapsin 2 inhibition.
• These findings provide insights for designing more potent memapsin 2 inhibitors for Alzheimer's disease therapy.