Agnes H. Henschen-Edman

cDNA Cloning and Primary Structure Analysis of C1qRP, the Human C1q/MBL/SPA Receptor That Mediates Enhanced Phagocytosis In Vitro

The complement protein C1q, mannose-binding lectin (MBL), and pulmonary surfactant protein A (SPA) are structurally similar molecules that enhance phagocytic function in vitro. Monoclonal antibodies R3 and R139, which inhibit the enhancement triggered by these three ligands, were used to purify a 126,000 M(r) cell surface protein designated C1qR(P). Amino acid sequence was obtained and the corresponding cDNA was cloned. C1qR(P) is a novel type I membrane protein with the following putative structural elements: a C-type carbohydrate recognition domain, five EGF-like domains, a transmembrane domain, and a short cytoplasmic tail. All peptides identified by amino acid sequencing are encoded by the cDNA. Additionally, an anti-peptide antiserum was generated, which is reactive with C1qR(P). The data indicate that the cloned cDNA encodes the receptor that plays a role in C1q/MBL/SPA-mediated removal or destruction of pathogens and immune complexes by phagocytosis.

Functional analysis of the α-defensin disulfide array in mouse cryptdin-4

The α-defensin antimicrobial peptide family is defined by a unique tridisulfide array. To test whether this invariant structural feature determines α-defensin bactericidal activity, mouse cryptdin-4 (Crp4) tertiary structure was disrupted by pairs of site-directed Ala for Cys substitutions. In a series of Crp4 disulfide variants whose cysteine connectivities were confirmed using NMR spectroscopy and mass spectrometry, mutagenesis did not induce loss of function. To the contrary, the in vitro bactericidal activities of several Crp4 disulfide variants were equivalent to or greater than those of native Crp4. Mouse Paneth cell α-defensins require the proteolytic activation of precursors by matrix metalloproteinase-7 (MMP-7), prompting an analysis of the relative sensitivities of native and mutant Crp4 and pro-Crp4 molecules to degradation by MMP-7. Although native Crp4 and the α-defensin moiety of proCrp4 resisted proteolysis completely, all disulfide variants were degraded extensively by MMP-7. Crp4 bactericidal activity was eliminated by MMP-7 cleavage. Thus, rather than determining α-defensin bactericidal activity, the Crp4 disulfide arrangement confers essential protection from degradation by this critical activating proteinase.

Fibrinogen Non‐Inherited Heterogeneity and Its Relationship to Function in Health and Disease

Abstract: In healthy individuals fibrinogen occurs in more than one million non‐identical forms because of the many possible combinations of biosynthetically or postbiosynthetically modified or genetically polymorphic sites. The various forms may show considerable differences in their functional properties. Normal variant sites are due to alternative splicing, modification of certain amino acid residues, and proteolysis. Both the Aα and the γ chain occur in two splice forms, and it is known that only the shorter γ chain can interact with platelets, but the longer may bind thrombin and factor XIII. Many types of posttranslationally modified amino acid residues are present in fibrinogen. The Aα chain is partially phosphorylated at two sites, possibly leading to protection against proteolysis. The Bβ chain is N‐glycosylated and partially proline hydroxylated, each at one site. The γ chain is N‐glycosylated at one site and the longer splice form doubly tyrosine‐sulfated. The glycosylations are believed to protect against polymerization and proteolysis. All three chains are partially oxidized at methionine residues and deamidated at asparagine and glutamine residues. The Aα and γ chain are partially carboxy‐terminally degraded by proteolysis, the shorter forms causing a decrease in polymerization, crosslinking, and clot stability. Abnormal variants occur in patients with diabetes mellitus, in the form of glycated lysine residues; in patients with certain types of cancer, in the form of crosslinked degradation products; in patients with certain types of autoimmune disease, in the form of complexes with antibodies; in cigarette smokers; and in individuals treated with acetylsalicylic acid, in the form of acetylated lysine residues.

Paneth Cell α-Defensins from Rhesus Macaque Small Intestine

ABSTRACT Antimicrobial peptides are secreted by small intestinal Paneth cells as components of innate immunity. To investigate the role of α-defensins in enteric host defenses in nonhuman primates, α-defensin cDNAs were isolated, α-defensin peptides were purified from rhesus macaque small bowel, and the bactericidal activities of the peptides were measured. Six rhesus enteric α-defensin (RED) cDNAs, RED-1 to RED-6, were identified in a jejunum cDNA library; the deduced RED peptides exhibited extensive diversity relative to the primary structures of rhesus myeloid α-defensins. RED-4 was purified from monkey jejunum, and N-terminal peptide sequencing of putative RED-4 peptides identified two N termini, RTCYCRTGR… and TCYCRTGRC…; these corresponded to alternative N termini for the RED-4 molecules, as deduced from their molecular masses and RED cDNAs. In situ hybridization experiments localized RED mRNAs exclusively to small intestinal Paneth cells. Recombinant RED-1 to RED-4 were purified to homogeneity and shown to be microbicidal in the low micromolar range (≤10 μg/ml) against gram-positive and gram-negative bacteria, with individual peptides exhibiting variable target cell specificities. Thus, compared to myeloid α-defensins from rhesus macaques, enteric α-defensin peptides are highly variable in both primary structure and activity. These studies should facilitate further analyses of the role of α-defensins in primate enteric immunity.

On the identification of beneficial and detrimental molecular forms of fibrinogen.

Fibrinogen is a central protein in blood coagulation. A functioning circulation system requires a precise balance between fibrin formation and removal, i.e. between the interaction of fibrin(ogen) with thrombogenic and fibrinolytic components of the blood. Fibrinogen and fibrin have also significant roles in wound healing, in tumor growth and metastasis as well as in defense mechanisms. All functions and interactions are mediated by specific structural elements of the molecule. Already in healthy individuals fibrinogen occurs in over a million nonidentical forms due to posttranslational modifications and genetic polymorphism. The various forms may show considerable differences in their functional properties. Alterations in distributions among preexisting forms as well as additional forms have been observed to accompany many types of disease. Furthermore, certain forms have been correlated with an increased risk to acquire disease. Monitoring the levels of various molecular forms is expected to be of considerable diagnostic and prognostic value in many types of disease.

Elevated Expression of Paneth Cell CRS4C in Ileitis-prone SAMP1/YitFc Mice REGIONAL DISTRIBUTION, SUBCELLULAR LOCALIZATION, AND MECHANISM OF ACTION

Paneth cells at the base of small intestinal crypts of Lieberkühn secrete host defense peptides and proteins, including α-defensins, as mediators of innate immunity. Mouse Paneth cells also express α-defensin-related Defcr-rs genes that code for cysteine-rich sequence 4C (CRS4C) peptides that have a unique CPX triplet repeat motif. In ileitis-prone SAMP1/YitFc mice, Paneth cell levels of CRS4C mRNAs and peptides are induced more than a 1000-fold relative to non-prone strains as early as 4 weeks of age, with the mRNA and peptide levels highest in distal ileum and below detection in duodenum. CRS4C-1 peptides are found exclusively in Paneth cells where they occur only in dense core granules and thus are secreted to function in the intestinal lumen. CRS4C bactericidal peptide activity is membrane-disruptive in that it permeabilizes Escherichia coli and induces rapid microbial cell K+ efflux, but in a manner different from mouse α-defensin cryptdin-4. In in vitro studies, inactive pro-CRS4C-1 is converted to bactericidal CRS4C-1 peptide by matrix metalloproteinase-7 (MMP-7) proteolysis of the precursor proregion at the same residue positions that MMP-7 activates mouse pro-α-defensins. The absence of processed CRS4C in protein extracts of MMP-7-null mouse ileum demonstrates the in vivo requirement for intracellular MMP-7 in pro-CRS4C processing.

Fibrinogen Longmont. A heterozygous abnormal fibrinogen with B beta Arg-166 to Cys substitution associated with defective fibrin polymerization.

Abstract: BβArg166 to Cys substitution was identified in an abnormal fibrinogen named fibrinogen Longmont. The proband, a young woman, and her mother were heterozygous; both experienced episodes of severe hemorrhage at childbirth. The neo‐Cys residues were found to be disulfide‐bridged to either an isolated Cys amino acid or to the corresponding Cys residue of another abnormal fibrinogen molecule, forming dimers. Thrombin and batroxobin induced fibrin polymerization were impaired, despite normal release of fibrinopeptides A and B. Moreover, the polymerization defect was not corrected by removing the dimeric species or adding calcium. Fibrinogen Longmont had normal polymerization site a, as evidenced by normal GPRP‐peptide binding. Thus, the sites A and a can interact to form protofibrils, as evidenced by dynamic light scattering measurements. These protofibrils, however, do not associate laterally in a normal manner, leading to an abnormal clot formation.

Four crystal forms of a Bence-Jones protein.

Four crystal forms have been grown and characterized by X-ray diffraction of a Bence-Jones protein collected from the urine of a multiple myeloma patient more than 40 years ago. Closely related tetragonal and orthorhombic forms belonging to space groups P4(3)2(1)2 and P2(1)2(1)2(1), with unit-cell parameters a = b = 68.7, c = 182.1 and a = 67.7, b = 69.4, c = 87.3 A, diffract to 1.5 and 1.9 A, respectively. Two closely related trigonal forms, both belonging to space group P3(1)21 with unit-cell parameters a = b = 154.3 A but differing by a doubling of the c axis, one 46.9 A and the other 94.0 A, diffract to 2.9 and 2.6 A resolution, respectively. The trigonal crystal of short c-axis length shows a positive indication of twinning. The trigonal crystal of longer c axis, which appeared only after eight months of incubation at room temperature, is likely to be composed of proteolytically degraded molecules and unlike the other crystal forms contains two entire Bence-Jones dimers in the asymmetric unit. This latter crystal form may shed some light on the formation of fibrils common to certain storage diseases.

HUMAN FIBRINOGEN OCCURS AS OVER 1 MILLION NON-IDENTICAL MOLECULES

Traditionally, proteins have been regarded as well-defined, uniform molecules, where one molecule is virtually identical to the next. This notion has been supported by the fact that the highly efficient protein primary structure analysis by prediction from the DNA sequence will result in a well-defined, unique amino acid sequence, containing no direct indication of any kind of modification or processing. However, information is accumulating about protein heterogeneity, co- or post-translational modification and processing as well as about the functional implications of the structural variation (Krishna and Wold, 1993; Graves et al., 1994). Human fibrinogen may serve as an extreme example of a protein existing in a multitude of structural forms, many of which have been demonstrated to differ in functional properties (Henschen and McDonagh, 1986; Henschen, 1993). In the following, the various, so far recognized structural variations and their possible function effects, together with some relevant identification procedures will be described.

Antifibrinogen IgG, fibrinogen, and Clq complexes circulating in a hypodysfibrinogenemic proband. Isolation, stoichiometry, and partial characterization.

Abstract: Circulating antifibrinogen antibodies have been reported in rare afibrinogenemic propositi, apparently occurring following fibrinogen replacement therapy, but immune complexes have not been described. In this report we describe circulating immune complexes formed by a monoclonal antifibrinogen IgG in a heterozygous hypodysfibrinogenemic (Aα 16 Arg → Cys) proband. Estimated by partial protein sequence and by other analyses, each immune complex consisted of one fibrin(ogen), one C1q, and 3–4 IgG molecules. The complexes were cryoprecipitable, a property also displayed by mixtures of proband IgG and normal fibrinogen. Indicating that both D and E domains were necessary for this behavior, cryoprecipitability was abolished by preincubation of the isolated IgG with either isolated normal fibrinogen fragment D100 or E. Consistent with the crossreactivity of the IgG with normal and mutant fibrinogen, the results suggest that the primary epitope resides on a D‐E locus on the fibrin polymer formed by normal and abnormal molecules containing the uncleaved (or mutant) peptide A.