Assembly process Insertion

A machine with approximately 1000 needles continuously produces a fabric 5-m wide. The assembly process is more complex, slower, and more expensive than tufting. The pile yam and stitch yam are inserted into the knitting needle, and the stuffer yam is interlocked with the others through a separate feed mechanism of the machine. As with tufting, the loops of the pile fabric formed are sHt, creating the desired individual blades. 

In this section we describe briefly the two models for inserting integral proteins into cell membranes with special emphasis on the protease(s)-catalyzed hydrolytic modification of these proteins associated with the membrane assembly process. These two models are (1) self assembly following translation of the proteins and (2) coupling of translation with insertion of the protein into the membrane. 

FeMo cofactor rasertion ( open conformation) involves at least the combined action of Fe protein, GroEL, MgATP, and possibly y 106-10 410,112 Once the FeMo cofactor site is accessible, the FeMo cofactor is inserted, y dissociates, and the assembly process of the matnre nitrogenase is completed. 

Fig. 2 Schematic illustration of chaperone/usher-assisted assembly of type 1 fimbriae. Subunits (A, F, G, H) enter the periplasm via the Sec system and transiently remain associated with the inner membrane (step 1). FimC chaperone (C) binds newly translocated, partially unfolded subunits to form soluble and stable chaperone subunit complexes (step 2). Targeting of the binary FimC FimH pre-assembly complex to an empty FimD usher (D) initiates assembly. At the usher, an incoming chaperone subunit complex attacks the chaperone subunit complex capping the base of the growing fibre (step 3). The usher catalyses DSE in which the capping chaperone at the base is released, the N-terminal Gd donor strand of the attacking subunit is inserted into the polymerization cleft of the subunit at the base to form a new fibre module, and a new chaperone-capped subunit is added at the base. For further details of the assembly process, see text...

For the most common types of biological clusters ([2Fe-2S], [3Fe-4S], and [4Fe-4S]), the assembly machinery includes iron chaperones, cysteine desulfurases, electron transfer proteins, molecular chaperones, and scaffold proteins on which the nascent cluster is assembled prior to insertion into a target protein. For the more complex and unusual clusters, such as FeMoco of nitrogenase, the [NiFe] center of hydrogenase, or the Fl-cluster of [FeFe] hydrogenase, significantly less is known about the cluster assembly process. As we shall discover below, one common theme that these systems share in the synthesis of their respective metallocofactors is the involvement of radical chemistry provided by radical SAM enzymes. 

The ubiquinol-cytochrome c oxidoreductase (cytochrome bc complex) of Rhodobacter sphaeroides is an integral component of the intracytoplasmic membrane (ICM) and functions in light-driven cyclic electron flow and the conservation of radiant energy as an electrochemical proton gradient. Previous studies on the assembly of electron transfer constituents in/ , sphaeroides have demonstrated that complete cycles of electron flow do not occur merely upon insertion of newly synthesized reaction centers at sites of initiation of ICM growth, but instead, subsequent synthesis and assembly of redox centers of the be complex are required [1]. To further characterize the assembly process and for detailed structural investigations, the complex was purified and antibodies were raised against the isolated polypeptide constituents. In this report, results on the localization and levels of the feCj complex in various membrane fractions are presented a detailed description of the structurd work will appear elsewhere [2]. 

Photosystem (PS) II in the procaryotic cyanobacteria is structurally similar to that in higher plants and contains around 20 different polypeptide subunits [1]. The reaction center of PSII, harboring the key components for the charge separation, consists of the D1 and D2 polypeptides [2,3]. Our studies concern the biogenesis of PSII in the cyanobacterium Synechocystis 6803. We are particularly interested in the role of the D1 polypeptide in the assembly process. We have previously described [4] the construction of a S. 6803 mutant where synthesis of the Dl polypeptide has been inactivated by insertional mutagenesis of the psbA gene family, encoding the Dl polypeptide. A preliminary functional characterization of that mutant showed that the PSII activity was severely perturbed while PSI activity was unaffected [4,5]. The structural analysis revealed that despite the lack of the Dl and D2 polypeptides, mutant thylakoids still retained several intrinsic PSII polypeptides [1]. 

When Lee and Subramanian invented the first fibrous transistor (Lee and Subramanian, 2003), they did not use it to develop a textile circuit. The reason may be in the rigidity, stability, and reproductivity of the fibrous transistor. The wire was in aluminum. It was difficult to insert it into woven fabric as a normal textile filament. Moreover, its evaporated semiconductor and source-drain electrodes were delicate. They would be easily destroyed during the assembly process. Besides, the source-drain electrodes were only in one side of the wire. The alignment with other conductive yams was a problem in the source-drain position. Even if this kind of fibrous transistor was ameliorated by using stainless wire as gate and depositing the source-drain around the whole wire (Lee and Subramanian, 2005 Maccioni et al., 2006), there still was no laboratory prototype of a fibrous transistor-based electronic circuit published. Because the deposition should be carried out in vacuum, it became impossible to exploit series manufacturing for... 

Figure 8 Schematic representation of the two-step self-assembly process of transmembrane peptides. The unstmctured protein segments insert into the membrane, followed by oligomer formation. Hexafluoroleucine residues are depicted as green spheres. Only the backbone (cylinder) and the core hydrophobic residues are shown for clarity.

In the case of automated assembly processes, the general sequence is part insertion followed by the soldering step. (Slightly different steps are used for the paste-in-hole process that is, the paste may be applied before or after part insertion.)... 

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