Calmodulin-dependent multifunctional protein kinase in Aspergillus nidulans

Area of Science:

• Biochemistry
• Molecular Biology
• Mycology

Background:

• Calcium/calmodulin-dependent protein kinases (CaM Kinasess) are crucial signaling enzymes.
• These kinases regulate diverse cellular processes in eukaryotes.
• Understanding fungal CaM Kinase function provides insights into conserved signaling.

Purpose of the Study:

• To isolate and characterize a Ca2+/calmodulin-dependent multifunctional protein kinase from Aspergillus nidulans.
• To determine its unique properties and substrate specificity.
• To investigate its relationship with known CaM Kinases.

Main Methods:

• Protein purification to homogeneity.
• Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (NaDodSO4/PAGE) for molecular weight determination.
• Two-dimensional isoelectric focusing/NaDodSO4/PAGE for analyzing enzyme forms.
• Calcium- and CaM-dependent autophosphorylation assays.
• Substrate phosphorylation assays using known CaM Kinase II substrates.
• Immunological cross-reactivity assays.

Main Results:

• A monomeric Ca2+/CaM-dependent multifunctional protein kinase was purified from Aspergillus nidulans.
• The enzyme exhibits autophosphorylation in a Ca2+/CaM-dependent manner, generating more acidic forms.
• It phosphorylates known substrates of type II Ca2+/CaM-dependent protein kinases.
• Cross-reactivity was observed with antiserum against rat brain protein kinase II.
• Isolated fungal calmodulin activated the kinase at lower concentrations than bovine calmodulin.

Conclusions:

• Aspergillus nidulans possesses a unique monomeric Ca2+/CaM-dependent protein kinase.
• This kinase shares functional and structural similarities with mammalian CaM Kinase II.
• The findings suggest conserved roles for Ca2+/CaM signaling pathways in fungi and animals.
• Fungal calmodulin may exhibit distinct activation properties for the native kinase.