Bodil Jönsson

Crystal structure of ferrochelatase: the terminal enzyme in heme biosynthesis

BACKGROUND The metallation of closed ring tetrapyrroles resulting in the formation of hemes, chlorophylls and vitamin B12 is catalyzed by specific enzymes called chelatases. Ferrochelatase catalyzes the terminal step in heme biosynthesis by inserting ferrous ion into protoporphyrin IX by a mechanism that is poorly understood. Mutations in the human gene for ferrochelatase can result in the disease erythropoietic protoporphyria, and a further understanding of the mechanism of this enzyme is therefore of clinical interest. No three-dimensional structure of a tetrapyrrole metallation enzyme has been available until now. RESULTS The three-dimensional structure of Bacillus subtilis ferrochelatase has been determined at 1.9 A resolution by the method of multiple isomorphous replacement. The structural model contains 308 of the 310 amino acid residues of the protein and 198 solvent molecules. The polypeptide is folded into two similar domains each with a four-stranded parallel beta sheet flanked by alpha helices. Structural elements from both domains build up a cleft, which contains several amino acid residues that are invariant in ferrochelatases from different organisms. In crystals soaked with gold and cadmium salt solutions, the metal ion was found to be coordinated to the conserved residue His 183, which is located in the cleft. This histidine residue has previously been suggested to be involved in ferrous ion binding. CONCLUSIONS Ferrochelatase seems to have a structurally conserved core region that is common to the enzyme from bacteria, plants and mammals. We propose that porphyrin binds in the identified cleft; this cleft also includes the metal-binding site of the enzyme. It is likely that the structure of the cleft region will have different conformations upon substrate binding and release.

A late Holocene lake sediment sequence from Livingston Island, South Shetland Islands, with palaeoclimatic implications

Analysis of a 1.5 m thick sediment sequence from Midge Lake, Byers Peninsula, Livingston Island, shows that the lake and its catchment have undergone significant changes during the last 4000 years. Radiocarbon dating (AMS), sediment lithology, and microfossil analyses indicate that the lake was deglaciated over 4000 14 C years ago. Distinct peaks in accumulation rates of sediment, Pediastrum algae, pollen and spores, as well as changes in the diatom assemblage, suggest significant environmental changes between ca 3200 and 2700 y BP. These changes are interpreted as reflecting a milder and more humid, maritime climate. The increased humidity can explain independent observations of glacier growth during this period. The combined data also indicate that between ca 1500 and 500 y BP the area might have experienced more continental conditions with slightly colder and drier climate than today. Since the 14 C dates from the Midge Lake sediments are regarded as reliable and the sediment sequence is rich in tephra layers this sediment sequence will be critical for a forthcoming tephra chronology of the region.

STRATIGRAPHIC AND PALEOCLIMATIC STUDIES OF A 5500-YEAR-OLD MOSS BANK ON ELEPHANT ISLAND, ANTARCTICA

Analyses of a core from the deepest known moss peat bank in Antarctica, on Elephant Island, South Shetlands, show that this Chorisodontium aciphyllum-dominated bank began to grow ca. 5500 14C yr BP. Combined with other studies in the region the present study indicates more extensive glaciation before 5000 to 6000 BP than today on some of the South Shetland Islands. The main hypothesis is that these frozen moss banks contain important paleoclimatic information. The stratigraphic parameters analyzed included degree of humification, organic and mineral matter content, bulk density, chronology, volumetric growth and organic accumulation rates, carbon and nitrogen concentrations, C/N ratios, nitrogen accumulation rates, and finally magnetic analyses to detect tephra horizons. A discussion of the interrelationships between these parameters is followed by theoretical calculations of annual net primary productivity combined with multivariate analysis of the data set. Results of the analysis show that three calculated productivity peaks coincide with three periods of milder and more humid summers, at 4150-3900, 3180-3030, and 2030-1840 BP. However, the period with possibly the warmest summers, 3180-3030 BP, is interpreted also to have been characterized by cold winters. The data suggest that the periods with the coldest summers (and possibly also winters) prevailed at the earliest stage of the moss bank development, at ca. 3500 BP, and 2500 BP.

Communication aids for people with aphasia

In principle, aphasia is a disability to use language. No wonder therefore, that most aphasiologists both in research and in therapy tend to focus mainly on linguistic function. The most prominent symptom of aphasia usually is a deficiency of speech, and many laymen believe that speech exercises should be the therapy of choice, which is not always correct. However, to those suffering from aphasia their disorder first of all means restricted communication and thereby a risk of becoming isolated. Therefore, besides language and speech therapy, people with aphasia have an urgent need of compensations or substitutes for their loss of communication. The number and variation of available communication aids for aphasia is rapidly increasing, mainly because of almost general use of computerized techniques. The following text wants to draw attention not only to software and hardware useful to aiding communication in aphasia, but also to the large amount of helpful information available from the Internet. Last but not least, access to the Internet as such may become an important tool to breaking isolation. A person with aphasia may need special arrangements and support, however, to be able to use her/his computer to this end, e.g. for e-mailing, web-surfing or chatting. Before the computers came into common use, a number of low-tech devices to aid communication were available. Amongst them may be mentioned letter boards, personal ‘passports’ for presentation of the owner and information about his/her problem, and photo albums used, for example, to raise new topics in a conversation. Comprehensive so-called communication books are described in detail by Millar (1,2). They may contain generalized picture and/or symbol vocabularies, guidance for conversation partners, index pages, etc., besides personal material such as photos, drawings, or newspaper cuttings. For different reasons, well discussed by van de Sandt-Konderman (3), low-tech communication aids for people with aphasia have not become very popular. One reason could be that much of the material is designed to suit mainly children or aims foremost at other types of communication problems than aphasia, such as. dysarthria (see for example (4,5)). Unfortunately this seems to be the case also for a number of high-tech communication aids. These are basically machines that can talk, either by a digitized or by a synthesized speech output. Digitized speech may be used to play back previously recorded entire messages. Synthesized speech has a lower quality but is more flexible, so that new messages may be phrased, as long as the user is able to do this and also to master correct spelling. The input to the aids may be indicated either by text or by graphics such as symbols, icons or pictures. The market abounds with this type of devices and the Swedish Institute for Handicap has listed no less than 36 such electrical speech aids (6 /9). High-tech aids specifically designed for aphasia may be divided in disorder oriented, ‘prosthetic’ systems, aiding specific problems such as those of word finding or sentence construction, and genuine conversation aids aiming at communicative function as a whole (3). Similar to the above mentioned communication books these later aids may be used to fulfil a number of different communicative needs such as presentation, claiming needs, asking questions, raising conversation topics, etc. Typically, these devices consist of a computer showing

Enabling communication: Pictures as language

A developmental disability often includes a language disorder, the result of which render learning, in part, if not entirely impossible. This has drastic consequences for children and adults, and gradually ends up becoming the primary disability. With to

Disclosing the Secrets of Braille Reading—Computer-Aided Registration and Interactive Analysis

The pilot project reported here utilized the first technology ever developed for the computerized on-line registration and analysis of finger movements during Braille reading. Five congenitally blind subjects performed tactile reading of pedagogically carefully selected texts. Two specialists in visual impairments analyzed the computer-registered reading activities using specially designed interaction software. The subjects themselves were interviewed and contributed to discussions about their own individual reading styles. The analyses of this first handful of subjects reveal a number of important strategies and preferences with regard to on-line tactile reading. Further, the results challenge several assumptions and practices in Braille teaching. This pilot project lays the foundation for more comprehensive large-scale studies—both cross-sectional and longitudinal ones—studies long wanted in the domain of tactile reading.

Enabling communication

Her background is in physics in which she received her Ph.D., taught and wrote textbooks. She has also contributed to public debate and written extensively on environmental concerns. Current areas of interest are IT and learning, especially the benefits of new technological and educational concepts for people with disabilities. She is in the process of establishing the research program, Pace-making, which focuses on stress-related illnesses, their causes, consequences and cures.

Ethics in the making

Applied ethics in research is no longer regarded as a concern exclusive to the medical field. Exemplars in ethics from other fields such as design are, however, meagre, as are relevant practical and design applied guidelines. The more ethically grounded a given area of research is, the greater the chance it can contribute to long-term, meaningful breakthroughs in knowledge. An improved ethics in design can enable a critical questioning that in turn leads to entirely new research questions.

The Liquid Drop: Exposing and Utilising Difference in the Design Process

Instead of discussing existing design methods that aim at bridging or annihilating gaps between users and designers, we want to highlight an approach for designers that helps us increase reflexivit ...