Posttranslational protein modification by polyamines in intact and regenerating nerves

Area of Science:

• Neuroscience
• Biochemistry
• Cell Biology

Background:

• Polyamines are essential molecules involved in various cellular processes.
• Protein modification by polyamines has been observed in other tissues.
• Nerve regeneration involves complex molecular changes.

Purpose of the Study:

• To investigate the covalent incorporation of polyamines into proteins in nerve tissues.
• To identify the enzymes responsible for polyamine-protein conjugation in nerves.
• To examine changes in this activity during nerve regeneration.

Main Methods:

• Preparation of nerve axoplasm supernatants from squid, rat, and goldfish.
• Incubation with radiolabeled polyamines ([3H]putrescine, [3H]spermidine) and exogenous protein.
• Enzyme inhibition studies using CuSO4.
• Analysis of enzyme kinetics, pH, and temperature optima.
• Polyacrylamide gel electrophoresis and analysis of protein-bound radioactivity.

Main Results:

• Nerve supernatants incorporated [3H]putrescine and [3H]spermidine into proteins.
• This incorporation was inhibited by CuSO4, suggesting transglutaminase involvement.
• Transglutaminase activity increased during nerve regeneration, with higher levels in non-axonal segments.
• Specific endogenous proteins (18, 46, 200 kDa) were labeled.
• The majority of activity in vertebrate nerves was found in non-neuronal cells.

Conclusions:

• Nerve tissues, particularly vertebrate nerves, exhibit transglutaminase-mediated covalent modification of proteins by polyamines.
• This activity is elevated during nerve regeneration.
• While axonal proteins may be modified, non-neuronal cells contribute significantly to polyamine-protein conjugation in nerves.