https://ucanr.edu/datastoreFiles/608-836.pdf

Pectin methylesterases: cell wall enzymes with important roles in plant physiology.

Pectin is a high value functional food ingredient widely used as a gelling agent and stabilizer. It is also an abundant, ubiquitous and multifunctional component of the cell walls of all land plants. Food scientists and plant scientists therefore share a common goal to better understand the structure and functionalities of pectic polymers at the molecular level. The basic properties of pectin have been known for nearly 200 years, but recently there has been tremendous progress in our understanding of the very complex fine structure of pectic polymers and pectinolytic enzymes. This has been made possible by synergies between plant and food research and by the application of a range of state-of-the-art techniques including enzymatic fingerprinting, mass spectrometry, NMR, molecular modelling, and monoclonal antibodies. With this increased knowledge comes the prospect of novel applications. Producers are beginning to develop a new generation of sophisticated designer pectins with specific functionalities. Moreover, the ability to manipulate pectin in planta would have a major impact on fruit and vegetable quality and processing, as well as on pectin production.

Pectin: new insights into an old polymer are starting to gel

New insights into pectin methylesterase structure and function.

1.1 Overview of the hyaluronidases
The hyaluronidases (Hyals) are classes of enzymes that degrade predominantly hyaluronan (HA). The term “hyaluronidase” is somewhat of a misnomer since they have the limited ability to degrade chondroitin (Ch) and chondroitin sulfates (ChS), albeit at a slower rate. It is a common misconception that the bacterial Hyals have absolute specificity for HA. This is incorrect. Both bacterial 1 and vertebrate enzymes degrade Ch and ChS, albeit at a slower rate. The plausible reason for this broader specificity is that chondroitins preceded HA in evolution. For example, the nematode, Caenorhabditis elegans, contains only Ch and no HA, with only one Hyal-like sequence (unpublished observations). This is most likely a chondroitinase. It is plausible, therefore, that the vertebrate Hyals evolved originally from pre-existing chondroitinases 1. This may explain why Hyals, recognizing their ancestral substrate, retain limited ability to also degrade Ch and ChS.

The Hyals from bacteria have been well characterized, and much information is available (for representative publications see 2–5). The Hyals in vertebrate tissues, on the other-hand, have not been studied extensively, however, due to the lack of structural information. Such studies were more difficult and, therefore, more limited. In addition, vertebrate Hyals are present at exceedingly low concentrations. In human serum, e.g., Hyal1 is present at 60 ng/ml 6. They have high specific activities that are unstable during the course of purification, requiring the constant presence of detergents and protease inhibitors for their isolation. Many of such difficulties have been overcome, and a great deal of information is now available, facilitated in part by the Human Genome Project 7.

Six Hyal sequences occur in the human genome, constituting a newly recognized family of enzymes. They have similar catalytic mechanisms that contrast markedly with the bacterial Hyals. There is growing interest in these enzymes as their HA substrate is achieving much attention. An outstanding review of the hyaluronidases was published 50 years ago by Karl Meyer, who was also the first to describe the chemical structure of HA 8. Interestingly, a chapter on mucopolysaccharidases, the former name for the hyaluronidases, was included in Volume 1 of Methods in Enzymology 9. The most recent overview of all of the Hyals appeared in 1971 10. Since that time, no comprehensive review has appeared.

Karl Meyer classified the Hyals into three distinct classes of enzymes 8, based entirely on the biochemical analyses available at the time. With the advent of sequence and structural data, we can now appreciate how remarkably accurate Karl Meyer’s classification scheme was. No modification of his formulation is necessary. There are three major groups of Hyals, based on their mechanisms of action. Two of the groups are endo-β-N-acetyl-hexosaminidases. One group includes the vertebrate enzymes that utilize substrate hydrolysis 11,12. The second group, which is predominantly bacterial, includes the eliminases that function by β-elimination of the glycosidic linkage with introduction of an unsaturated bond 2–4,13–17. As these enzymes catalyze the breaking of chemical bond by means other than hydrolysis or oxidation, and with the forming a new double bond they are also termed lyases. Both terms, the eliminase (or β-eliminase) and the lyase, are used in the review interchangeably. The third group are the endo-β-glucuronidases. These are found in leeches, which are annelids 18, and in certain crustaceans 19. No sequence data are available, and little is known about this potentially interesting class of enzymes. However, their mechanism of action resembles that of the eukaryotic or vertebrate enzymes more closely than the bacterial enzymes.

Sequence data for vertebrate Hyals now provide opportunities to formulate structure-function relationships, to examine probable mechanisms of catalysis, to identify putative substrate binding sites, and to consider the additional non-enzymatic functions of this family of multifunctional enzymes for two of the three groups, for the hydrolase and lyase types of Hyals, respectively 2. Such a review is presented here, documenting some of the common and some of the unusual features that distinguish each of these families of enzymes.

The primary objective of this review is to clarify what is known about the structure and mode of action of all the Hyals. Since so little is known of the leech-type of Hyals, the β-endoglucuronidases, the emphasis will, by necessity, be upon two of the three classes of enzymes. Other aspects of these enzymes, such as their physiological activities, their dependence on reaction conditions, their role in cell biology and involvement in metabolism, and their use as reagents or as therapeutics, are not the concern presently. A review of these other aspects of the Hyals will appear separately (Stern and Jedrzejas, in preparation).

High levels of HA turnover occur in vertebrate tissues. Tight regulation of catabolism is crucial for modulating steady state levels, important for normal homeostasis, and for embryonic development, wound healing, regeneration, and repair. Under pathological conditions, as in severe stress, shock, septicemia, in burn patients, following major surgery, massive injury, circulating HA levels increases rapidly. HA also increases in association with aggressive malignancies. Determining the mechanism of action of the Hyals is critical for understanding their controls over such a wide range of functions (for reviews, see 20,21).

/pdf/hyaluronidases-their-genomics-structures-and-mechanisms-of-3lts34acqe.pdf

Hyaluronidases: their genomics, structures, and mechanisms of action.

Pseudomonas aeruginosa thrives in many aqueous environments and is an opportunistic pathogen that can cause both acute and chronic infections. Environmental conditions and host defenses cause differing stresses on the bacteria, and to survive in vastly different environments, P. aeruginosa must be able to adapt to its surroundings. One strategy for bacterial adaptation is to self-encapsulate with matrix material, primarily composed of secreted extracellular polysaccharides. P. aeruginosa has the genetic capacity to produce at least three secreted polysaccharides; alginate, Psl, and Pel. These polysaccharides differ in chemical structure and in their biosynthetic mechanisms. Since alginate is often associated with chronic pulmonary infections, its biosynthetic pathway is the best characterized. However, alginate is only produced by a subset of P. aeruginosa strains. Most environmental and other clinical isolates secrete either Pel or Psl. Little information is available on the biosynthesis of these polysaccharides. Here, we review the literature on the alginate biosynthetic pathway, with emphasis on recent findings describing the structure of alginate biosynthetic proteins. This information combined with the characterization of the domain architecture of proteins encoded on the Psl and Pel operons allowed us to make predictive models for the biosynthesis of these two polysaccharides. The results indicate that alginate and Pel share certain features, including some biosynthetic proteins with structurally or functionally similar properties. In contrast, Psl biosynthesis resembles the EPS/CPS capsular biosynthesis pathway of Escherichia coli, where the Psl pentameric subunits are assembled in association with an isoprenoid lipid carrier. These models and the environmental cues that cause the cells to produce predominantly one polysaccharide over the others are subjects of current investigation.

/pdf/biosynthesis-of-the-pseudomonas-aeruginosa-extracellular-4seihg1udf.pdf

Biosynthesis of the Pseudomonas aeruginosa Extracellular Polysaccharides, Alginate, Pel, and Psl

Crystal structure of polygalacturonase from Erwinia carotovora ssp. carotovora.

Three-dimensional structure of Erwinia chrysanthemi pectin methylesterase reveals a novel esterase active site.

A new photoconductor device structure is described utilizing a heterojunction contact which incorporates a higher band‐gap HgCdTe alloy between the metal contact and the normal band‐gap photoconductor. A theoretical treatment of the heterojunction contact photoconductor (HCP) device shows that carrier sweepout can be virtually eliminated; the calculations predict elimination of ‘‘saturation’’ of responsivity and a very large increase in responsivity. HCP devices were fabricated; experimental results verified the theory in several ways. A responsivity was measured at 80 K of about 450 000 V/W at 30 V/cm and over 1 500 000 V/W at 125 V/cm.

HgCdTe heterojunction contact photoconductor

We present an experimental and theoretical study of n‐type Hg1−xCdxTe photoconductors in which a large band‐gap alloy was grown on top of a smaller band‐gap active region and contacts were made to the larger gap material. The larger band‐gap material causes an energy barrier to holes which decreases the rate at which they reach the high recombination region of the metal‐semiconductor interface. As a result, this heterojunction contact greatly reduces the effects of carrier sweepout on device performance and leads to much higher detector responsivities. Experimental results in a symmetric device with a cutoff wavelength of 7.8 μm at 77 K show responsivities in excess of 106 V/W and detectivities close to the background limited value and nonsaturation of responsivity with bias voltage. In an asymmetric device, in which only one heterojunction contact was used, an order of magnitude increase in responsivity was observed when the heterojunction contact was biased to attract minority carriers, compared with th...

Drummond Smith

Papers

Crystal structure of polygalacturonase from Erwinia carotovora ssp. carotovora.

Three-dimensional structure of Erwinia chrysanthemi pectin methylesterase reveals a novel esterase active site.

HgCdTe heterojunction contact photoconductor

High responsivity HgCdTe heterojunction photoconductor

Polygalacturonase from erwinia carotovora ssp. carotovora