Protein tyrosine phosphatases are regulated by mononuclear iron dicitrate

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Macrophages are crucial in infectious diseases and iron homeostasis.
• Previous work showed iron-dependent inhibition of macrophage protein-tyrosine phosphatase (PTP) activity.
• The specific molecular mechanism of this inhibition was previously unknown.

Purpose of the Study:

• To identify the iron-containing species responsible for inhibiting macrophage PTP activity.
• To elucidate the mechanism by which this species inhibits PTP.
• To investigate the functional consequences of this inhibition on cellular signaling.

Main Methods:

• Biochemical assays to identify the inhibitory iron complex.
• Computational modeling to understand the interaction between the iron complex and PTP.
• In vitro and in vivo experiments to assess the effects of iron-citrate on protein phosphorylation and MAPK signaling.

Main Results:

• The mononuclear dicitrate iron complex [Fe(cit)(2)H(4-x)]((1+x)-) was identified as the inhibitor.
• This iron-citrate complex ([Fe(cit)(2)](5-)) competitively inhibits the PTP SHP-1 by targeting its catalytic pocket.
• Inhibition of PTP activity by iron-citrate leads to protein hyperphosphorylation and enhanced MAPK signaling in response to LPS.

Conclusions:

• Iron-citrate is a specific inhibitor of macrophage PTP activity.
• This inhibition occurs through competitive binding to the SHP-1 catalytic pocket.
• Iron-citrate-mediated PTP inhibition represents a novel regulatory mechanism for signal transduction, impacting immune responses.