Chlorosomes are unique light-harvesting structures found in two families of photosynthetic bacteria. In this study, three chlorosome proteins (CsmF, CsmH, and CsmX) of the green sulfur bacterium Chlorobium tepidum were characterized by cloning and sequencing the genes which encode them, by overproducing the respective proteins in Escherichia coli, and by raising polyclonal antisera to the purified proteins. Three other proteins (AtpF, CT1970, and CT2144) which were identified in chlorosome fractions have similarly been characterized. The antisera were used to establish the distribution of each protein in various cellular fractions. Ten chlorosome proteins (CsmA, CsmB, CsmC, CsmD, CsmE, CsmF, CsmH, CsmI, CsmJ, and CsmX) copurified in a constant proportion together with bacteriochlorophyll c, and none of these 10 proteins was found in substantial amounts in other subcellular fractions. An antiserum to CsmH was highly effective in agglutinating chlorosomes, and antisera to CsmI, CsmJ, CsmX, and CsmA also immunoprecipitated chlorosomes to varying extents. However, an antiserum to CsmF did not agglutinate chlorosomes. The sequences of chlorosome proteins generally are not significantly similar to the sequences of other proteins in the databases. However, the N-terminal domains of three chlorosome proteins, CsmI, CsmJ, and CsmX, are related to adrenodoxin-type ferredoxins that ligate [2Fe-2S] clusters [Vassilieva, E. V., Antonkine, M. L., Zybailov, B. L., Yang, F., Jakobs, C. U., Golbeck, J. H., and Bryant, D. A. (2001) Biochemistry 40, 464-473]. The sequences of the C-terminal domains of these three proteins appear to be distantly related to CsmA and CsmE. The remaining chlorosome proteins can be divided into two additional structural families, CsmB/F and CsmC/D. CsmH is recovered in water-soluble form after overproduction in E. coli. Interestingly, this protein contains an N-terminal domain that is similar to CsmB/D, while its C-terminal domain is related to CsmC/D. The sequence relationships indicate that, although the protein composition of Chlorobium-type chlorosomes is superficially more complex than that of the chlorosomes of Chloroflexus aurantiacus, this heterogeneity is mostly produced by gene duplication and divergence among a small number of protein types.

L-Serine deaminases catalyze the deamination of Lserine, producing pyruvate and ammonia. Two families of these proteins have been described and are delineated by the cofactor that each employs in catalysis. These are the pyridoxal 5 -phosphate-dependent deaminases and the deaminases that are activated in vitro by iron and dithiothreitol. In contrast to the enzymes that employ pyridoxal 5 -phosphate, detailed physical and mechanistic characterization of the iron-dependent deaminases is limited, primarily because of their extreme instability. We report here the characterization of L-serine deaminase from Escherichia coli, which is the product of the sdaA gene. When purified anaerobically, the isolated protein contains 1.86 ؎ 0.46 eq of iron and 0.670 ؎ 0.019 eq of sulfide per polypeptide and displays a UV-visible spectrum that is consistent with a [4Fe-4S] cluster. Reconstitution of the protein with iron and sulfide generates considerably more of the cluster, and treatment of the reconstituted protein with dithionite gives rise to an axial EPR spectrum, displaying gʈ ‫؍‬ 2.03 and g Ќ ‫؍‬ 1.93. Mö ssbauer spectra of the 57 Fe-reconstituted protein reveal that the majority of the iron is in the form of [4Fe-4S] 2؉ clusters, as evidenced by the typical Mö ssbauer parameters-isomer shift, ␦ ‫؍‬ 0.47 mm/s, quadrupole splitting of ⌬E Q ‫؍‬ 1.14 mm/s, and a diamagnetic (S ‫؍‬ 0) ground state. Treatment of the dithionitereduced protein with L-serine results in a slight broadening of the feature at g ‫؍‬ 2.03 in the EPR spectrum of the protein, and a dramatic loss in signal intensity, suggesting that the amino acid interacts directly with the cluster.

The monitoring of the levels of alloantibodies following transplantation might facilitate early diagnosis of chronic rejection (CR), the leading cause of renal allograft failure. Here, we used serial alloantibody surveillance to monitor patients with preoperative positive flow cytometric crossmatch (FCXM). Sixty-nine of 308 renal transplant patients in our center had preoperative positive FCXM. Blood was collected quarterly during the first postoperative year and tested by FCXM and single antigen bead luminometry, more sensitive techniques than complement-dependent cytotoxic crossmatching. Distinct post-transplant profiles emerged and were associated with different clinical outcomes. Two-thirds of patients showed complete elimination of FCXM and solid-phase assay reactions within 1 year, had few adverse events, and a 95% 3-year graft survival. In contrast, the remaining third failed to eliminate flow FCXM or solid-phase reactions directed against HLA class I or II antibodies. The inferior graft survival (67%) with loss in this latter group was primarily due to CR. Thus, systematic assessment of longitudinal changes in alloantibody levels, either by FCXM or solid-phase assay, can help identify patients at greater risk of developing CR.

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Heterozgyous spondyloepiphyseal dysplasia congenita (sedc/+) mice expressing a missense mutation in col2a1 exhibit a normal skeletal morphology but early-onset osteoarthritis (OA). We have recently examined knee articular cartilage obtained from homozygous (sedc/sedc) mice, which express a Stickler-like phenotype including dwarfism. We examined sedc/sedc mice at various levels to better understand the mechanistic process resulting in OA. Mutant sedc/sedc, and control (+/+) cartilages were compared at two, six and nine months of age. Tissues were fixed, decalcified, processed to paraffin sections, and stained with hematoxylin/eosin and safranin O/fast green. Samples were analyzed under the light microscope and the modified Mankin and OARSI scoring system was used to quantify the OA-like changes. Knees were stained with 1C10 antibody to detect the presence and distribution of type II collagen. Electron microscopy was used to study chondrocyte morphology and collagen fibril diameter. Compared with controls, mutant articular cartilage displayed decreased fibril diameter concomitant with increases in size of the pericellular space, Mankin and OARSI scores, cartilage thickness, chondrocyte clustering, proteoglycan staining and horizontal fissuring. In conclusion, homozygous sedc mice are subject to early-onset knee OA. We conclude that collagen in the mutant’s articular cartilage (both heterozygote and homozygote) fails to provide the normal meshwork required for matrix integrity and overall cartilage stability.