| 1. |
- Al-Karadaghi, Salam, et al.
(author)
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A decade of progress in understanding the structural basis of protein synthesis
- 2000
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In: Progress in Biophysics and Molecular Biology. - 1873-1732. ; 73:2, s. 167-193
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Research review (peer-reviewed)abstract
- The key reaction of protein synthesis, peptidyl transfer, is catalysed in all living organisms by the ribosome - an advanced and highly efficient molecular machine. During the last decade extensive X-ray crystallographic and NMR studies of the three-dimensional structure of ribosomal proteins, ribosomal RNA components and their complexes with ribosomal proteins, and of several translation factors in different functional states have taken us to a new level of understanding of the mechanism of function of the protein synthesis machinery. Among the new remarkable features revealed by structural studies, is the mimicry of the tRNA molecule by elongation factor G, ribosomal recycling factor and the eukaryotic release factor 1. Several other translation factors, for which three-dimensional structures are not yet known, are also expected to show some form of tRNA mimicry. The efforts of several crystallographic and biochemical groups have resulted in the determination by X-ray crystallography of the structures of the 30S and 50S subunits at moderate resolution, and of the structure of the 70S subunit both by X-ray crystallography and cryo-electron microscopy (EM). In addition, low resolution cryo-EM models of the ribosome with different translation factors and tRNA have been obtained. The new ribosomal models allowed for the first time a clear identification of the functional centres of the ribosome and of the binding sites for tRNA and ribosomal proteins with known three-dimensional structure. The new structural data have opened a way for the design of new experiments aimed at deeper understanding at an atomic level of the dynamics of the system.
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| 2. |
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| 3. |
- Fedorov, R V, et al.
(author)
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Structure of ribosomal protein TL5 complexed with RNA provides new insights into the CTC family of stress proteins
- 2001
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In: Acta Crystallographica. Section D: Biological Crystallography. - 1399-0047. ; D57:7, s. 968-976
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Journal article (peer-reviewed)abstract
- The crystal structure of Thermus thermophilus ribosomal protein TL5 in complex with a fragment of Escherichia coli 5S rRNA has been determined at 2.3 Å resolution. The protein consists of two domains. The structure of the N-terminal domain is close to the structure of E. coli ribosomal protein L25, but the C-terminal domain represents a new fold composed of seven -strands connected by long loops. TL5 binds to the RNA through its N-terminal domain, whereas the C-terminal domain is not included in this interaction. Cd2+ ions, the presence of which improved the crystal quality significantly, bind only to the protein component of the complex and stabilize the protein molecule itself and the interactions between the two molecules in the asymmetric unit of the crystal. The TL5 sequence reveals homology to the so-called general stress protein CTC. The hydrophobic cores which stabilize both TL5 domains are highly conserved in CTC proteins. Thus, all CTC proteins may fold with a topology close to that of TL5.
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| 4. |
- Kristensen, Fredrik, et al.
(author)
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A Flexible FFT Processor
- 2002
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Conference paper (peer-reviewed)abstract
- In this paper a flexible FFT processor for OFDM systems is presented. In future wireless systems using OFDM each terminal should be able to handle a wide range of different applications, from pure voice communication to high-speed data transfers, with as little overhead in power consumption and protocol procedure as possible. As the terminals will be battery powered and should be cheap to manufacture an ASIC solution is required. To be able to adapt to different communication schemes and various communication channels the FFT processor must be configurable. To minimize power consumption no more precision than necessary should be used. A pipelined radix22 FFT processor, with the possibility of run time switching between 32-1024 points, have been designed in a standard CMOS 0.35 µm technology. Clock gating and low power memories have been used to reduce power consumption.
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| 5. |
- Kristensen, Fredrik, et al.
(author)
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A Generic Transmitter for Wireless OFDM Systems
- 2003
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In: 14th IEEE Proceedings on Personal, Indoor and Mobile Radio Communications, 2003. PIMRC 2003.. - 0780378229 ; 3, s. 2234-2238
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Conference paper (peer-reviewed)
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| 6. |
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| 7. |
- Kristensen, Fredrik, et al.
(author)
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Flexible baseband transmitter for OFDM
- 2003
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In: Proceedings of the IASTED International Conference on Circuits, Signals, and Systems. - 0889863512 ; , s. 356-361
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Conference paper (peer-reviewed)abstract
- To fully utilize the available spectrum for a wireless communication system it is feasible to adapt to different situations on the channel. In this paper a flexible OFDM transmitter is presented together with basic theory behind OFDM transmission. It is shown that high flexibility can be obtained with a reasonable amount of additional hardware. Part of the design, the FFT-processor, has already been fabricated and measurement results are presented.
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| 8. |
- Kristensen, Fredrik, et al.
(author)
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Reduced transceiver-delay for OFDM systems
- 2004
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In: 2004 IEEE 59th Vehicular Technology Conference. VTC 2004-Spring. - 0780382552 ; , s. 1242-1245
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Conference paper (peer-reviewed)abstract
- In this paper, it is shown that more than half of the data flow buffer, due to a bit reversed FFT output and cyclic prefix in an OFDM transceiver, can be removed. To achieve this, a new pipelined FFT processor is proposed and a cyclic suffix is used instead of the more commonly used cyclic prefix. The FFT processor is used either with a forward or backward data flow, i.e. performing either a decimation in time or a decimation in frequency FFT. However, this approach precludes wordlength optimization in the processor and therefore a semi floating-point arithmetic is used to achieve high signal-to-noise ratio. Total delay through the transceiver is reduced by 25% and for larger transceivers silicon area is reduced by as much as 25%. In addition, the proposed scheme reduces the required amount of memory accesses to insert a cyclic extension, and has the basic properties of a simple interleaver
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| 9. |
- Kristensen, O, et al.
(author)
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Is tRNA binding or tRNA mimicry mandatory for translation factors?
- 2002
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In: Current Protein and Peptide Science. - 1875-5550. ; 3:1, s. 133-141
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Research review (peer-reviewed)abstract
- tRNA is the adaptor in the translation process. The ribosome has three sites for tRNA, the: A-, P-, and E-sites. The tRNAs bridge between the ribosomal subunits with the decoding site and the mRNA on the small or 30S subunit and the peptidyl transfer site on the large or 50S subunit. The possibility that, translation release factors could mimic tRNA has been discussed for a long time, since their function is very similar to that of tRNA. They identify stop codons of the mRNA presented in the decoding site and hydrolyse the nascent peptide from the peptidyl tRNA in the peptidyl transfer site. The structures of eubacterial release factors are not yet known, and the first example of tRNA mimicry was discovered when elongation factor G (EF-G) was found to have a closely similar shape to a complex of elongation factor Tu (EF-Tu) with aminoacyl-tRNA. An even closer imitation of the tRNA shape is seen in ribosome recycling factor (RRF). The number of proteins mimicking tRNA is rapidly increasing. This primarily concerns translation factors. It is now evident that in some sense they are either tRNA mimics, GTPases or possibly both.
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| 10. |
- Kristensen, O, et al.
(author)
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Structural characterization of the stringent response related exopolyphosphatase/guanosine pentaphosphate phosphohydrolase protein family
- 2004
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In: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 43:28, s. 8894-8900
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Journal article (peer-reviewed)abstract
- Exopolyphosphatase/guanosine pentaphosphate phosphohydrolase (PPX/GPPA) enzymes play central roles in the bacterial stringent response induced by starvation. The high-resolution crystal structure of the putative Aquifex aeolicus PPX/GPPA phosphatase from the actin-like ATPase domain superfamily has been determined, providing the first insights to features of the common catalytic core of the PPX/GPPA family. The protein has a two-domain structure with an active site located in the interdomain cleft. Two crystal forms were investigated (type I and 11) at resolutions of 1.53 and 2.15 Angstrom, respectively. This revealed a structural flexibility that has previously been described as a "butterfly-like" cleft opening around the active site in other actin-like superfamily proteins. A calcium ion is observed at the center of this region in type I crystals, substantiating that PPX/GPPA enzymes use metal ions for catalysis. Structural analysis suggests that nucleotides bind at a similar position to that seen in other members of the superfamily.
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