Chlorophyll breakdown in higher plants.

Chlorophyll breakdown is an important catabolic process of leaf senescence and fruit ripening. Structure elucidation of colorless linear tetrapyrroles as (final) breakdown products of chlorophyll was crucial for the recent delineation of a chlorophyll breakdown pathway which is highly conserved in land plants. Pheophorbide a oxygenase is the key enzyme responsible for opening of the chlorin macrocycle of pheophorbide a characteristic to all further breakdown products. Degradation of chlorophyll was rationalized by the need of a senescing cell to detoxify the potentially phototoxic pigment, yet recent investigations in leaves and fruits indicate that chlorophyll catabolites could have physiological roles. This review updates structural information of chlorophyll catabolites and the biochemical reactions involved in their formation, and discusses the significance of chlorophyll breakdown. This article is part of a Special Issue entitled: Regulation of Electron Transport in Chloroplasts

Identification of a novel family of proteins in snake venoms. Purification and structural characterization of nawaprin from Naja nigricollis snake venom

10.1074/jbc.M305322200Journal of Biological Chemistry2784140097-40104JBCH

Update on the biochemistry of chlorophyll breakdown

In land plants, chlorophyll is broken down to colorless linear tetrapyrroles in a highly conserved multi-step pathway. The pathway is termed the 'PAO pathway', because the opening of the chlorine macrocycle present in chlorophyll catalyzed by pheophorbide a oxygenase (PAO), the key enzyme of the pathway, provides the characteristic structural basis found in all further downstream chlorophyll breakdown products. To date, most of the biochemical steps of the PAO pathway have been elucidated and genes encoding many of the chlorophyll catabolic enzymes been identified. This review summarizes the current knowledge on the biochemistry of the PAO pathway and provides insight into recent progress made in the field that indicates that the pathway is more complex than thought in the past

On the use of pseudocontact shifts in the structure determination of metalloproteins

The utility of pseudocontact shifts in the structure refinement of metalloproteins has been evaluated using a native, paramagnetic Cu2+ metalloprotein, plastocyanin from Anabaena variabilis (A.v.), as a model protein. First, the possibility of detecting signals of nuclei spatially close to the paramagnetic metal ion is investigated using the WEFT pulse sequence in combination with the conventional TOCSY and 1H-15N HSQC sequences. Second, the importance of the electrical charge of the metal ion for the determination of correct pseudocontact shifts from the obtained chemical shifts is evaluated. Thus, using both the Cu+ plastocyanin and Cd2+-substituted plastocyanin as the diamagnetic references, it is found that the Cd2+-substituted protein with the same electrical charge of the metal ion as the paramagnetic Cu2+ plastocyanin provides the most appropriate diamagnetic reference signals. Third, it is found that reliable pseudocontact shifts cannot be obtained from the chemical shifts of the 15N nuclei in plastocyanin, most likely because these shifts are highly dependent on even minor differences in the structure of the paramagnetic and diamagnetic proteins. Finally, the quality of the obtained 1H pseudocontact shifts, as well as the possibility of improving the accuracy of the obtained structure, is demonstrated by incorporating the shifts as restraints in a refinement of the solution structure of A.v. plastocyanin. It is found that incorporation of the pseudocontact shifts enhances the precision of the structure in regions with only few NOE restraints and improves the accuracy of the overall structure. Copyright © 2006 John Wiley & Sons, Ltd