Tailless keratins assemble into regular intermediate filaments in vitro

Area of Science:

• Cell Biology
• Biochemistry
• Structural Biology

Background:

• Keratins are intermediate filament proteins crucial for cellular structure.
• The non alpha-helical tail domain's role in keratin filament formation is not fully understood.

Purpose of the Study:

• To investigate the influence of the non alpha-helical tail domain of keratin 8 on filament formation.
• To determine if keratin tail domains are essential for in vitro filament assembly.

Main Methods:

• Site-directed mutagenesis was used to create a truncated keratin 8 mutant (K8/tailless) lacking its tail domain.
• Purification of the K8/tailless mutant from Escherichia coli.
• In vitro reconstitution assays were performed using K8/tailless with wild-type K18 and K19.

Main Results:

• The truncated K8/tailless mutant, when reconstituted with K18, demonstrated filament formation.
• Reconstitution experiments with K8/tailless and K19 (a naturally tailless keratin I) confirmed filament assembly.
• These results indicate that the C-terminal tail domain is not required for in vitro filament formation in both type I and type II keratins.

Conclusions:

• The non alpha-helical tail domains of both type I and type II keratins are not essential for in vitro filament formation.
• In vitro filament elongation appears independent of head and tail domain interactions.
• Tail domains may play a role in stabilizing intermediate filaments formed by specific keratin pairs.