Fibulin-4 Accelerates Amyloid Formation by Binding with a Keratin 5 Peptide Fragment

Area of Science:

• Dermatology
• Biochemistry
• Molecular Biology

Background:

• Keratins are primary amyloid components in localized cutaneous amyloidosis.
• Understanding the specific molecular interactions driving amyloid formation is crucial for disease insight.

Purpose of the Study:

• To identify the specific keratin fragments involved in localized cutaneous amyloidosis.
• To investigate the role of fibulin-4 in keratin-induced amyloid formation.

Main Methods:

• Immunohistochemical staining of patient skin samples using antibodies against extracellular matrix proteins and keratin 5 (K5).
• Screening of 14 synthetic peptides from K5's C-terminal region for amyloidogenic properties using thioflavin T staining and β-sheet structure analysis.
• Assessing the binding affinity and amyloid formation acceleration between K5-derived peptides and fibulin-4.

Main Results:

• Keratin 5 (K5) and fibulin-4 were found to colocalize within amyloid deposits in localized cutaneous amyloidosis.
• Two K5-derived peptides exhibited amyloidogenic properties, forming β-sheet structures and amyloid-like fibrils.
• A specific K5 peptide (KT5-6) from the α-helical rod domain directly bound to fibulin-4, and fibulin-4 accelerated its amyloid formation.

Conclusions:

• Degraded fragments of K5, particularly those containing the KT5-6 sequence, can form amyloid fibrils in conjunction with fibulin-4.
• These K5 fragments and fibulin-4 represent potential initiators of cutaneous amyloidosis.
• The findings provide new molecular insights into the pathogenesis of localized cutaneous amyloidosis.