The vacuole-type ATPases (V-ATPases) exist in various intracellular compartments of eukaryotic cells to regulate physiological processes by controlling the acidic environment. The crystal structure of the subunit C of Thermus thermophilus V-ATPase, homologous to eukaryotic subunit d of V-ATPases, has been determined at 1.95-Å resolution and located into the holoenzyme complex structure obtained by single particle analysis as suggested by the results of subunit cross-linking experiments. The result shows that VATPase is substantially longer than the related F-type ATPase, due to the insertion of subunit C between the V 1 (soluble) and the Vo (membrane bound) domains. Subunit C, attached to the Vo domain, seems to have a socket like function in attaching the central-stalk subunits of the V 1 domain. This architecture seems essential for the reversible association͞dissociation of the V 1 and the Vo domains, unique for V-ATPase activity regulation.T he vacuole-type ATPases (V-ATPases) are commonly found in many organisms involved in a variety of physiological processes (1). V-ATPases in eukaryotic cells (eukaryotic VATPases) translocate protons across the membrane consuming ATP. They reside within intracellular compartments, including endosomes, lysosomes, and secretory vesicles, and within plasma membranes of certain cells including renal intercalated cells, osteoclasts, and macrophages. Eukaryotic V-ATPases are responsible for various cell functions including the acidification of intracellular compartments, renal acidification, born resorption, and tumor metastasis (2).V-ATPase and the F-type ATP synthase (F-ATPase) are evolutionary related and share the rotary mechanism coupling ATP synthesis͞hydrolysis and proton translocation across the membrane (2-4). However, these two types of ATPase show significant differences. Reversible association͞dissociation of the V 1 domain (soluble) and the V o domain (membrane bound) is a unique activity regulation mechanism compared to FATPase (Fig. 1). For example, glucose deprivation has been shown to cause a rapid dissociation of the yeast V-ATPase into free V 1 and V o domains, which is reversible and independent of de novo protein synthesis (5, 6). Similar observations have been reported for Manduca sexta and mammalian complexes (7-9). Subunit composition and structure in the stalk region of VATPase, which connects the V o and V 1 domains, are suggested to be significantly different from those in F-ATPase (10) (Fig. 1). Thus, this region is possibly responsible for the association͞ dissociation of the complex.V-ATPases are also found in archaea and some eubacteria (prokaryotic V-ATPases) (11). The V-ATPase from Thermus thermophilus is solely responsible for aerobic ATP synthesis in this bacteria, which lacks F-ATPase (12). The Thermus VATPase is composed of nine different subunits, which are arranged within the atp operon in the order of G-I-L-E-C-F-A-B-D, which encodes proteins with molecular sizes of 13, 71,8,20,35,12, 64, 54, and 25 kDa, respectively (10) (Fig. 1). This A...

The membrane-bound respiratory complex II, succinate:ubiquinone oxidoreductase (SQR) from Escherichia coli, has been anaerobically expressed, then purified and crystallized. The initial crystals obtained were small and diffracted poorly. In order to facilitate structure determination, rational screening and sample-quality analysis using electron microscopy was implemented. The crystals of SQR from E. coli belong to the trigonal space group R32, with unit-cell parameters a = b = 138.7, c = 521.9 A, and diffract to 2.6 A resolution. The optimization strategy used for obtaining well diffracting SQR crystals is applicable to a wide range of membrane proteins.

IL-2 has a major role in the activation, differentiation and growth of several distinct lineages of hematopoietic cells. IL-2 has effects on other cell types as squamous tumour cells, melanoma and renal cancer. The IL-2 delivers a growth signal through a specific receptor (IL-2R) which binds IL-2 with high affinity. We have detected the presence of the functional three subunits of IL-2R in two cervical carcinoma cell lines. In normal lymphocytes, the IL-2 signal transduction through phosphorylation of protein tyrosine kinases appears to be critical for lymphocyte proliferation. However, the role of IL-2R on the signal transduction events in cervical cancer cells has not been investigated. In order to identify the proteins associated with the induction of proliferation of the cervical cancer cell lines, CALO and INBL, we evaluated the effect of IL-2 on tyrosine phosphorylation of JAK kinases. In the present work we demonstrate that JAK3 is phosphorylated in response to IL-2 within 30 seconds and the activation ceases at 1 minute. We also found that JAKl is associated with phosphorylated p and y subunits, but is not phosphorylated in response to IL-2. Our data suggest that signaling through the 1L-2R in CALO and INBL cells could be similar to the early signaling events in normal lymphocytes.The light-induced reception of signal and transduction is conducted by the photoreceptor structure in the eye. Phototransduction has been studied in both vertebrates and invertebrates, including squid (Loligo forbesi). The invertebrate phototransduction involves the activation of the phosphatidylinositol-4, 5 -bisphosphate pathway. Phototransduction in squid photoreceptors involves a series of proteins, including sTRP (a 92 kDa protein) and cytoskeletal components. An interesting characteristic of sTRP is its interaction with some of the cytoskeletal proteins. The major cytoskeletal components are the 140 kDa, 150 kDa proteins and actin. Information obtained so far indicates that the 140 kDa protein has no obvious homology with other known proteins while the 150 kDa protein has some similarity to myosins, class-I and V and to the unconventional myosin NINAC (product of the neither inactivation nor after potential C gene) which is involved in the photoresponse of rosophila. An interesting feature of the 140 kDa protein is the presence of a PAEK repeat toward its carboxyterminal region. Preliminary NMR experiments on a tetrapeptide containing the PAEK repeat suggest an extended-type structure; proline residues prevent it from being a regular helix. This section of the protein is possibly involved in the formation of bridge structures extending from microvillar core to the membrane.The Ser/Thr kinase PDK-1 (3-phosphoinositide dependent protein kinase-1) was originally identified for its ability to phosphorylate and activate protein kinase B (PKB/Akt). Through binding of its carboxyterminal pleckstrin homology (PH) domain to phosphatidylinositol 3,4,5-trisphosphate and phosphatidylinositol3,4-bisphosphate, PDK-1 translocates to the ...

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