Molecular identifiers of the evolutionarily conserved titin pseudokinase

Area of Science:

• Muscle physiology and molecular biology
• Protein structure and function
• Evolutionary biology

Background:

• Titin kinase (TK) is a vertebrate-specific pseudokinase found in striated muscle sarcomeres.
• TK is hypothesized to function as a mechanoreceptor, sensing mechanical signals during muscle activity.
• Previous research on TK has primarily focused on the human form, with its phosphotransfer activity being uncertain.

Purpose of the Study:

• To determine if the pseudokinase nature of TK is conserved across different species.
• To investigate the evolutionary conservation of TK's functional motifs and flanking regions.
• To propose a classification for fish titin genes (ttna and ttnb isoforms).

Main Methods:

• Comparative sequence analysis of distantly evolved fish TK representatives.
• Determination of the crystal structure of medaka TK (isoform b).
• Sequence clustering analysis for TK subgroup identification and gene classification.

Main Results:

• Evolutionarily conserved sequence deviations in ATP and magnesium binding motifs (θxK and EFG) confirm TK's pseudokinase character.
• N- and C-terminal flanking tails exhibit structural similarity across orthologues, with conserved sequence motifs (YD-motif, [R/K]H[R/K]RYY, R-7x-R).
• Mammalian TKs show a unique inhibitory interaction not observed in fish; fish titin genes classified into ttna and ttnb isoforms.

Conclusions:

• The pseudokinase signature of TK is conserved across vertebrates, characterized by specific sequence deviations and conserved flanking tail structures.
• The identified conserved motifs and structural similarities provide insights into TK's mechanosensory role.
• A novel classification of fish titin genes into ttna and ttnb isoforms is proposed, facilitating future research.