A comparison of cryptophytan phycocyanins.

Area of Science:

• Biochemistry
• Phycology
• Spectroscopy

Background:

• Phycocyanins are vital biliproteins in cryptophytes, essential for photosynthesis.
• Hemiselmis virescens exhibits strain-specific phycocyanin variations.
• Understanding these variations is key to cryptophyte evolutionary studies.

Purpose of the Study:

• To purify and compare phycocyanins from two Hemiselmis virescens strains (Millport 64 and Plymouth 157).
• To elucidate the structural and chromophoric differences contributing to spectroscopic variations.
• To characterize the unique chromophore composition of Millport 64 phycocyanin.

Main Methods:

• Purification of phycocyanins from Millport 64 and Plymouth 157 strains.
• Native molecular weight determination.
• Subunit analysis (alpha and beta subunits) and molecular weight estimation.
• Spectroscopic analysis, including absorption maxima determination for chromophores.

Main Results:

• Both strains possess phycocyanins with similar native molecular weights and subunit structures (alpha and beta subunits).
• Phycocyanin from Plymouth 157 has two bilins per subunit (maxima at 600 and 660 nm).
• Millport 64 phycocyanin's beta subunit has these chromophores, but its alpha subunit has a different chromophore (maxima at 368 and 694 nm).
• This difference in chromophore composition fully explains the observed spectroscopic variations between the two phycocyanins.
• Millport 64 phycocyanin is the first described biliprotein containing three distinct chemical chromophores.

Conclusions:

• Spectroscopic differences in Hemiselmis virescens phycocyanins are driven by distinct chromophore compositions.
• The Millport 64 strain harbors a unique biliprotein with three chemically different chromophores.
• This finding expands the known diversity of biliprotein structures and functions.