Di¡erential glycosylation and proteolytical processing of LeechCAM in
central and peripheral leech neurons
Chunfa Jie
a
, Birgit Zipser
b
, John Jellies
c
, Kristen M. Johansen
a
, JÖrgen Johansen
aY
*
a
Department of Zoology and Genetics, 3156 Molecular Biology Building, Iowa State University, Ames, IA 50011, USA
b
Department of Physiology, Michigan State University, East Lansing, MI 48824, USA
c
Department of Biological Sciences, Western Michigan University, Kalamazoo, MI 49008, USA
Received 19 May 1999; received in revised form 5 August 1999; accepted 5 August 1999
Abstract
LeechCAM is a recently described member of the Ig-superfamily which has five Ig-domains, two FNIII-domains, a
transmembrane domain, and a cytoplasmic domain. Phylogenetic analysis indicated that LeechCAM is the leech homolog of
apCAM, FasII, and vertebrate NCAM. Using a leechCAM-specific monoclonal antibody we show by immunoblot analysis
and by Triton X-114 phase separation experiments that in addition to existing in a transmembrane version LeechCAM is
likely to be proteolytically cleaved into a secreted form without the transmembrane domain and the intracellular tail.
Furthermore, by immunoprecipitation we demonstrate that LeechCAM is glycosylated with the Laz2-369 glycoepitope, an
epitope that has been specifically implicated in regulation of axonal outgrowth and synapse formation. ß 1999 Elsevier
Science B.V. All rights reserved.
Keywords: LeechCAM; Di¡erential glycosylation ; Proteolytic processing; Neuron; (Leech)
1. Introduction
Glycosylated cell adhesion molecules (CAMs) are
expressed on the surface of axons and growth cones
and fall into several structural classes, most notably
the immunoglobulin (Ig)-superfamily, the cadherins,
and the integrins. The combined activities of these
molecules are required to facilitate growth cone ex-
tension and synapse formation and to maintain the
complexity of mature neural structures [1]. They have
also been implicated in higher order processes such
as synaptic plasticity underlying learning and mem-
ory [2,3]. An important feature of the molecular
structure of the neural CAMs of the Ig-superfamily
is the variability of their extracellular regions which
in most cases contain multiple tandemly arranged
domains [4]. This kind of modular composition al-
lows them to interact with an array of di¡erent pro-
teins. In addition, the diversity in the structure of
neural CAMs is ampli¢ed with the existence of
many splice variants and various post-translational
modi¢cations such as di¡erential glycosylation and
proteolytic processing [5,6].
We have recently cloned and identi¢ed a new
member of the Ig-superfamily in the nervous system
of the leech, LeechCAM, which contains ¢ve Ig- and
two FNIII-domains, a transmembrane domain, and
an intracellular tail [7]. LeechCAM is one of two
di¡erent members of the Ig-superfamily in leech,
the other being Tractin, which were identi¢ed based
0167-4889 / 99 / $ ^ see front matter ß 1999 Elsevier Science B.V. All rights reserved.
PII: S0167-4889(99)00118-4
* Corresponding author. Fax: +1-515-294-0345;
E-mail: jorgen@iastate.edu
BBAMCR 14543 28-10-99
Biochimica et Biophysica Acta 1452 (1999) 161^171
www.elsevier.com/locate/bba