Is Point in Attribute of Model Class possible?

This is an xml schema for requesting a WebMethod:

  <RetrieveClienteRequest>
     <model query="">
        <keys query="" >
           <cliente.cnpj type="String"></cliente.cnpj>
        </keys>
        <instance>
           <cliente.cnpj type="String"></cliente.cnpj>
        </instance>
     </model>
  </RetrieveClienteRequest>

The WebMethod:

[WebMethod]
public XmlDocument RetrieveClienteRequest(model model)
{
    XmlDocument xmlDoc = new XmlDocument();
    ClienteBusiness objClienteBusiness = new ClienteBusiness();
    xmlDoc = objClienteBusiness.getCustomer(model);
    return xmlDoc;
}

The problem is that the client.cnpj attribute has period (.) and in the Model Class there can not be period , how to get around it?

I have tried this:

public class keys
    {
        [Column("cliente.cnpj"), Display(Name = "cliente.cnpj")]
        public string cliente_cnpj { get; set; }
    }

I am using SoapUI to do test and the client_cnpj attribute comes with the "_" and can not, has to return with "." (Score).

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:tem="http://tempuri.org/">
   <soapenv:Header/>
   <soapenv:Body>
      <tem:RetrieveClienteRequest>
         <tem:model>
            <tem:Keys>
               <tem:cliente_cnpj>?</tem:cliente_cnpj>
            </tem:Keys>
            <tem:instance>
               <tem:cliente_cnpj>?</tem:cliente_cnpj>
            </tem:instance>
         </tem:model>
      </tem:RetrieveClienteRequest>
   </soapenv:Body>
</soapenv:Envelope>