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K C Holmes

Publications and source records attributed to K C Holmes.

At least 19 recordsLinked to original sources
PubMed2004

The structure of the rigor complex and its implications for the power stroke.

Decorated actin provides a model system for studying the strong interaction between actin and myosin. Cryo-energy-filter electron microscopy has recently yielded a 14 A resolution map of rabbit skeletal actin decorated with chicken skeletal S1. The crystal structure of the cross-bridge from skeletal chicken myosin could not be fitted into the three-dimensional electron microscope map without some deformation. However, a newly published structure of the nucleotide-free myosin V cross-bridge, which is apparently already in the strong binding form, can be fitted into the three-dimensional reconstruction without distortion. This supports the notion that nucleotide-free myosin V is an excellent model for strongly bound myosin and allows us to describe the actin-myosin interface. In myosin V the switch 2 element is closed although the lever arm is down (post-power stroke). Therefore, it appears likely that switch 2 does not open very much during the power stroke. The myosin V structure also differs from the chicken skeletal myosin structure in the nucleotide-binding site and the degree of bending of the backbone beta-sheet. These suggest a mechanism for the control of the power stroke by strong actin binding.

Actins↗
PubMed2004

Introduction.

Explore the source record for details and available documents.

Actins↗
PubMed2000

The structural basis of muscle contraction.

The myosin cross-bridge exists in two conformations, which differ in the orientation of a long lever arm. Since the lever arm undergoes a 60 degree rotation between the two conformations, which would lead to a displacement of the myosin filament of about 11 nm, the transition between these two states has been associated with the elementary 'power stroke' of muscle. Moreover, this rotation is coupled with changes in the active site (CLOSED to OPEN), which probably enable phosphate release. The transition CLOSED to OPEN appears to be brought about by actin binding. However, kinetics shows that the binding of myosin to actin is a two-step process which affects both ATP and ADP affinity and vice versa. The structural basis of these effects is only partially explained by the presently known conformers of myosin. Therefore, additional states of the myosin cross-bridge should exist. Indeed, cryoelectron microscopy has revealed other angles of the lever arm induced by ADP binding to a smooth muscle actin-myosin complex.

Actins↗
PubMed1999

Structural biology.

Protein crystallography has become a major technique for understanding cellular processes. This has come about through great advances in the technology of data collection and interpretation, particularly the use of synchrotron radiation. The ability to express eukaryotic genes in Escherichia coli is also important. Analysis of known structures shows that all proteins are built from about 1000 primeval folds. The collection of all primeval folds provides a basis for predicting structure from sequence. At present about 450 are known. Of the presently sequenced genomes only a fraction can be related to known proteins on the basis of sequence alone. Attempts are being made to determine all (or as many as possible) of the structures from some bacterial genomes in the expectation that structure will point to function more reliably than does sequence. Membrane proteins present a special problem. The next 20 years may see the experimental determination of another 40,000 protein structures. This will make considerable demands on synchrotron sources and will require many more biochemists than are currently available. The availability of massive structure databases will alter the way biochemistry is done.

Crystallography, X-Ray↗
PubMed1999

Role of the salt-bridge between switch-1 and switch-2 of Dictyostelium myosin.

Motifs N2 and N3, also referred to as switch-1 and switch-2, form part of the active site of molecular motors such as myosins and kinesins. In the case of myosin, N3 is thought to act as a gamma-phosphate sensor and moves almost 6 A relative to N2 during the catalysed turnover of ATP, opening and closing the active site surrounding the gamma-phosphate. The closed form seems to be necessary for hydrolysis and is stabilised by the formation of a salt-bridge between an arginine residue in N2 and a glutamate residue in N3. We examined the role of this salt-bridge in Dictyostelium discoideum myosin. Myosin motor domains with mutations E459R or R238E, that block salt-bridge formation, show defects in nucleotide-binding, reduced rates of ATP hydrolysis and a tenfold reduction in actin affinity. Inversion of the salt-bridge in double-mutant M765-IS eliminates most of the defects observed for the single mutants. With the exception of a 2,500-fold higher KMvalue for ATP, the double-mutant displayed enzymatic and functional properties very similar to those of the wild-type protein. Our results reveal that, independent of its orientation, the salt-bridge is required to support efficient ATP hydrolysis, normal communication between different functional regions of the myosin head, and motor function.

Adenosine Diphosphate↗
PubMed1999

Structural mechanism of muscle contraction.

X-ray crystallography shows the myosin cross-bridge to exist in two conformations, the beginning and end of the "power stroke." A long lever-arm undergoes a 60 degrees to 70 degrees rotation between the two states. This rotation is coupled with changes in the active site (OPEN to CLOSED) and phosphate release. Actin binding mediates the transition from CLOSED to OPEN. Kinetics shows that the binding of myosin to actin is a two-step process which affects ATP and ADP affinity. The structural basis of these effects is not explained by the presently known conformers of myosin. Therefore, other states of the myosin cross-bridge must exist. Moreover, cryoelectronmicroscopy has revealed other angles of the cross-bridge lever arm induced by ADP binding. These structural states are presently being characterized by site-directed mutagenesis coupled with kinetic analysis.

Actins↗
PubMed1999

Medical student database development: a model for record management in a multi-departmental setting.

Student records flow through medical school offices at a rapid rate. Much of this data is often tracked on paper, spread across multiple departments. The Medical Student Informatics Group at the University of Utah School of Medicine identified offices and organizations documenting student information. We assessed departmental needs, identified records, and researched database software available within the private sector and academic community. Although a host of database applications exist, few publications discuss database models for storage and retrieval of student records. We developed and deployed an Internet based application to meet current requirements, and allow for future expandability. During a test period, users were polled regarding utility, security, stability, ease of use, data accuracy, and potential project expansion. Feedback demonstrated widespread approval, and considerable interest in additional feature development. This experience suggests that many medical schools would benefit from centralized database management of student records.

Consumer Behavior↗
PubMed1998

A molecular model for muscle contraction.

The molecular mechanism of muscle contraction has been elucidated by a combination of electron microscopy, biochemistry and X-ray diffraction from fibres and crystals. Protein crystallography provided the essential molecular anatomy for understanding this problem. Synchrotron radiation has played a crucial role.

Animals↗
PubMed1998

How X-ray Diffraction with Synchrotron Radiation Got Started.

The need to record low-angle-scattering X-ray fibre diagrams from muscle with millisecond time resolution drove the use of synchrotron radiation as an X-ray light source. The first smudgy diffraction patterns were obtained from a slice of insect flight muscle. Out of this grew the EMBL Outstation at DESY.

Journal Article↗
PubMed1998

Muscle contraction.

Understanding muscle contraction goes to the heart of one of the fundamental questions posed by classical philosophy, namely the nature of the pi nu epsilon upsilon mu alpha psi nu chi iota kappa omicron nu. The nature of 'understanding' has altered greatly during the last two millenia, particularly in response to the development of the concept of energy. Moreover, understanding contraction depends on understanding muscle structure. Galen was the first to make a detailed anatomical examination of the mode of action of muscles and recognized the heart as a muscle, but this line of research was not pursued until Leonardo da Vinci rediscovered it 1400 years later. Vesalius used the phrase Machina Carnis, but it was first Descartes who proposed a neuromuscular machine. However, the level of understanding of the physiology of muscle depends critically on the resolution of the available anatomy. Radical new insight was provided by electron microscopy. But an understanding at a physicochemical level is only possible if the structures of the components are known at atomic resolution. These have become known in the last five years and have led to dramatic progress. The present level of understanding of muscle is a physicochemical explanation of how the hydrolysis of ATP by the component proteins actin and myosin leads to movement.

Actins↗
PubMed1997

Development of Synchrotron Radiation as a High-Intensity Source for X-ray Diffraction.

Interest in the molecular mechanism of muscle contraction led to the search for an intense source of X-rays of 1-2 A wavelength so as to be able to examine the rich X-ray diffraction patterns given by muscles during contraction. This led to the first X-ray diffraction experiments using synchrotron radiation, carried out by Holmes, Rosenbaum and Witz at DESY, Hamburg, in September 1970. In the following years, the EMBL Outstation, to utilize synchrotron radiation for biological structure determination, was established at DESY and preliminary experiments on muscle were also carried out at NINA (Daresbury). The development of time-resolved techniques for muscle diffraction was first started in the MRC Molecular Biology Laboratory in Cambridge, using rotating-anode X-ray tubes, and was then greatly extended at the EMBL Outstation, Hamburg, using the storage ring DORIS. This was a very successful venture, and helped to drive the whole technology development and to interest other potential users in the technique.

Journal Article↗
PubMed1997

The swinging lever-arm hypothesis of muscle contraction.

The molecular mechanism of muscle contraction is a problem that has exercised biophysicists and biochemists for many years. The common view of the mechanism is embodied in the 'cross-bridge hypothesis', in which the relative sliding of thick (myosin) and thin (actin) filaments in cross-striated muscle is brought about by the 'cross-bridges', parts of the myosin molecules which protrude from the thick filaments and interact cyclically with the actin filaments, transporting them by a rowing action that is powered by the hydrolysis of ATP. This hypothesis is, however, rather vague on the molecular details of cross-bridge movement and, in the light of the recently determined crystal structures of myosin and actin, it has evolved into the more precise 'swinging lever-arm hypothesis'.

Actins↗
PubMed1996

Muscle proteins--their actions and interactions.

Muscle contracts by the myosin cross-bridges "rowing' the actin filaments past the myosin filaments. In the past year many structural details of this mechanism have become clear. Structural studies indicate distinct states for myosin S1 in the rigor, ATP or "down' conformation and in the products complex (ADP.Pi) or "up' to state. Crystallographic studies substantiate this classification and yield details of the transformation. The isomerization "up' to "down' is the power stroke of muscle. This consists in the main of large changes of angle of the "lever arm' (at the distal part of the myosin head) which can account for an 11 nm power stroke.

Actomyosin↗