PARENT SESSION
Posters P4Aa Chlorophyll and bilin based antenna systems. Abstracts (239-271)

Isolation of two biochemically different fucoxanthin-chlorophyll complexes from diatoms by ion exchange chromatography. Martin Lohr¹, Fey Holger², Claudia Büchel^*,2, ¹ Institute of General Botany, Mainz, Germany² Max Planck Institute of Biophysics, Frankfurt, Germany

ABSTRACT- Like vascular plants, the eukaryotic diatoms possess only membrane-intrinsic antenna proteins. These show high sequence homology to other light-harvesting complexes (LHC), e.g. from vascular plants. The polypeptides from diatoms are considerably smaller in size (in the range of 17 to 23 kDa) due to a truncated N- and C-terminus and shorter loops. Like the LHC-proteins, the antenna from diatoms binds Chl a but the accessory Chl b is replaced by Chl c. Instead of lutein and neoxanthin, the main carotenoids are fucoxanthin and diadinoxanthin. Previously, two different antenna proteins (fucoxanthin-chlorophyll proteins, FCP) were isolated in a functional state from the centric diatom Cyclotella meneghiniana by means of sucrose density centrifugation and gel filtration. The two FCPs differed in their polypeptide composition and oligomeric state. Trimers consisted of either 18 kDa or 19 kDa polypeptides, but only trimers composed of 19 kDa were assembled into stable higher oligomers (Büchel, Biochemistry 42, 13027-13034, 2003). Here, we report on a method using anion exchange chromatography to isolate the different FCPs in one step, improving yield and purity. The FCPs showed the same oligomeric state as described previously and were functionally intact as proven by absorption-, fluorescence- and CD-spectroscopy. In another diatom, Phaeodactylum tricornutum, the major FCP is encoded by five genes (fcpA-E) with considerable sequences homology to the 18kDa proteins of C. cryptica, a close relative of C. menegheniana. A search of the EST data base of P. tricornutum identified sequences for proteins more closely related to the 19 kDa proteins than to the 18 kDa proteins of C. cryptica. Using the same separation method as for the FCPs of C. meneghiniana, two FCP proteins could be isolated from P. tricornutum, one resembling the major FCP reported frequently and another FCP, which differed in pI and molecular weight.

KEY WORDS: carotenoids, bacillariophyceae, thylakoids, heterokont algae