Carcinoembryonic antigen cell adhesion molecule 1 (CEACAM1) structure and uses thereof in drug identification and screening

#CEACAM1 is a member of the carcinoembryonic antigen (CEA) family. Isoforms of murine CEACAM1 serve as receptors for mouse hepatitis virus (MHV), a murine coronavirus.

#Carcinoembryonic antigen (CEA; CD66e) was initially discovered as a tumor antigen (Gold and Freedman, 1965). A large group of related glycoproteins is now called the CEA family within Ig superfamily (IgSF). These anchored or secreted glycoproteins are expressed by epithelial cells, leukocytes, endothelial cells and placenta (Hammarstrom, 1999). In humans, the CEA family contains 29 genes or pseudogenes. The revised nomenclature of this family of glycoproteins was recently summarized (Beauchemin et al., 1999). The CEA family consists of the CEACAM (CEA-related cell adhesion molecule) and PSG (pregnancy-specific glycoprotein) subfamilies whose proteins share many common structural features (Hammarstrom, 1999).

#CEACAM1 (CD66a) is the most highly conserved member of the CEA family. Most species have only one CEACAM1 gene, but mice have two closely related genes called CEACAM1 and CEACAM2 (Beauchemin et al., 1999). CEACAM1 has many important biological functions. It is a potent vascular endothelial growth factor (Ergun et al., 2000) and a growth inhibitor in tumor cells (Izzi et al., 1999); plays a key role in differentiation of mammary glands (Huang et al., 1999); is an early marker of T cell activation; and modulates the functions of murine T lymphocytes (Morales et al., 1999; Nakajima et al., 2002). Human CEACAM1 is one of several human CEACAM proteins that serve as receptors for virulent strains of Neisseria gonorrhoeae, Neisseria meningitidis, and Hemophilus influenzae (Bos et al., 1999; Virji et al., 2000; Virji et al., 1999).

#FIG. 1. Stereo view of the ribbon drawing of msCEACAM1a [1,4] which contains two Ig-like domains. The CC′-loop in the N-terminal domain (D1) which is involved in binding of MHV and other ligands is highlighted in yellow. The predicted key virus-binding residue Ile41 on the CC′ loop is shown in ball-and-stick style. The FG loop of D1, another biologically important element is also shown. The carbohydrate moieties are drawn in ball-and-stick style. The glycan at Asn70 that is conserved in the whole CEA family is labeled. The figure was prepared using MOLSCRIPT®(Krulis, 1991).

#FIG. 2(A)-2(C). Superposition of D1 of msCEACAM1a[1,4], CD2, CD4 and Bence-Jones protein REI. Each molecule is shown in Cα trace, with msCEACAM1a in cyan, CD2 in purple, CD4 in brown and REI in green, respectively. The uniquely convoluted conformation of the CC′ loop in msCEACAM1a[1,4] is striking. The sequence alignment of the CC′ loop regions of these four molecules are also shown using the same code. (2B) Stereo view of the exposed residues on the CFG face of D1 of msCEACAM1a[1,4]. The Cu. trace of the CC′ loop is highlighted. Displayed sidechains and carbohydrates are drawn in ball-and-stick style. (2C) Change the legend to “Electrostatic potential surface representation of the same view as (B). The electrostatic potential is colored blue for positive and red for negative, and was calculated in the absence of carbohydrates and solvent molecules. FIGS. 2A and B were prepared with MOLSCRIPT® (Krulis, 1991), and 2C, with GRASP® (Nicholls et al., 1991).

#FIG. 3. A comparative view of structures of several virus receptors, including msCEACAM1a, receptor for murine coronavirus MHV; ICAM1, receptor for the major group of rhinoviruses; CD4, primary receptor for HIV; and CD46, receptor for measles virus. Shown here are only their N-terminal domains. Their key virus-binding motifs with uniquely topological features are also highlighted.

#The present invention is illustrated in further detail by the following non-limiting examples. Although the following descriptions re directed to preferred embodiments, namely a molecular model useful for designing compounds that modulate the interaction between the novel structure of the CC′ loop of the carcinoembryonic antigen cell adhesion molecule and other molecules (e.g. antibodies), as well as the various compounds that will satisfy this criteria, it should be understood that this description is illustrated only and is not intended to limit the scope of the invention.

#The amino acid residues described herein are preferred to be in the “L” isomeric form. However, residues in the “D” isomeric form can be substituted for any L-amino acid residue, as long as the desired fractional property of immunoglobulin-binding is retained by the polypeptide. NH.sub.2 refers to the free amino group present at the amino terminus of a polypeptide. COOH refers to the free carboxy group present at the carboxy terminus of a polypeptide. In keeping with standard polypeptide nomenclature, J. Biol. Chem., 243:3552-59 (1969), abbreviations for amino acid residues are shown in the following Table of Correspondence: 2 TABLE OF CORRESPONDENCE SYMBOL 1-Letter 3-Letter AMINO ACID Y Tyr tyrosine G Gly glycine F Phe phenylalanine M Met methionine A Ala alanine S Ser serine I Ile isoleucine L Leu leucine T Thr threonine V Val valine P Pro proline K Lys lysine H His histidine Q Gln glutamine E Glu glutamic acid W Trp tryptophan R Arg arginine D Asp aspartic acid N Asn asparagine C Cys cysteine

#It should be noted that all amino-acid residue sequences are represented herein by formulae whose left and right orientation is in the conventional direction of amino-terminus to carboxy-terminus. Furthermore, it should be noted that a dash at the beginning or end of an amino acid residue sequence indicates a peptide bond to a further sequence of one or more amino-acid residues. The above Table is presented to correlate the three-letter and one-letter notations which may appear alternately herein.